PLT-7503: Create Message Export Scheduled Task and CLI Command (#7612)

* Created message export scheduled task

* Added CLI command to immediately kick off an export job

* Added email addresses for users joining and leaving the channel to the export

* Added support for both MySQL and PostgreSQL

* Fixing gofmt error

* Added a new ChannelMemberHistory store and associated tests

* Updating the ChannelMemberHistory channel as users create/join/leave channels

* Added user email to the message export object so it can be included in the actiance export xml

* Don't fail to log a leave event if a corresponding join event wasn't logged

* Adding copyright notices

* Adding message export settings to daily diagnostics report

* Added System Console integration for message export

* Cleaned up TODOs

* Made batch size configurable

* Added export from timestamp to CLI command

* Made ChannelMemberHistory table updates best effort

* Added a context-based timeout option to the message export CLI

* Minor PR updates/improvements

* Removed unnecessary fields from MessageExport object to reduce query overhead

* Removed JSON functions from the message export query in an effort to optimize performance

* Changed the way that channel member history queries and purges work to better account for edge cases

* Fixing a test I missed with the last refactor

* Added file copy functionality to file backend, improved config validation, added default config values

* Fixed file copy tests

* More concise use of the testing libraries

* Fixed context leak error

* Changed default export path to correctly place an 'export' directory under the 'data' directory

* Can't delete records from a read replica

* Fixed copy file tests

* Start job workers when license is applied, if configured to do so

* Suggestions from the PR

* Moar unit tests

* Fixed test imports

i18n/en.json

@@ -1332,6 +1332,10 @@
     "id": "api.file.move_file.configured.app_error",
     "translation": "File storage not configured properly. Please configure for either S3 or local server file storage."
   },
+  {
+    "id": "api.file.move_file.copy_within_s3.app_error",
+    "translation": "Unable to copy file within S3."
+  },
   {
     "id": "api.file.move_file.delete_from_s3.app_error",
     "translation": "Unable to delete file from S3."
@@ -3850,6 +3854,18 @@
     "id": "ent.data_retention.generic.license.error",
     "translation": "License does not support Data Retention."
   },
+  {
+    "id": "ent.message_export.generic.license.error",
+    "translation": "License does not support Message Export."
+  },
+  {
+    "id": "ent.elasticsearch.start.create_bulk_processor_failed.app_error",
+    "translation": "Failed to create Elasticsearch bulk processor"
+  },
+  {
+    "id": "ent.elasticsearch.start.start_bulk_processor_failed.app_error",
+    "translation": "Failed to start Elasticsearch bulk processor"
+  },
   {
     "id": "ent.elasticsearch.aggregator_worker.create_index_job.error",
     "translation": "Elasticsearch aggregator worker failed to create the indexing job"
@@ -4378,6 +4394,54 @@
     "id": "model.channel_member.is_valid.user_id.app_error",
     "translation": "Invalid user id"
   },
+  {
+    "id": "model.channel_member_history.is_valid.channel_id.app_error",
+    "translation": "Invalid channel id"
+  },
+  {
+    "id": "model.channel_member_history.is_valid.user_id.app_error",
+    "translation": "Invalid user id"
+  },
+  {
+    "id": "model.channel_member_history.is_valid.user_email.app_error",
+    "translation": "Invalid user email"
+  },
+  {
+    "id": "model.channel_member_history.is_valid.join_time.app_error",
+    "translation": "Invalid join time"
+  },
+  {
+    "id": "model.channel_member_history.is_valid.leave_time.app_error",
+    "translation": "Invalid leave time"
+  },
+  {
+    "id": "store.sql_channel_member_history.log_join_event.app_error",
+    "translation": "Failed to record channel member history"
+  },
+  {
+    "id": "store.sql_channel_member_history.log_leave_event.select_error",
+    "translation": "Failed to record channel member history. No existing join record found"
+  },
+  {
+    "id": "store.sql_channel_member_history.log_leave_event.update_error",
+    "translation": "Failed to record channel member history. Failed to update existing join record"
+  },
+  {
+    "id": "store.sql_channel_member_history.get_users_in_channel_at.app_error",
+    "translation": "Failed to get users in channel at specified time"
+  },
+  {
+    "id": "store.sql_channel_member_history.get_users_in_channel_during.app_error",
+    "translation": "Failed to get users in channel during specified time period"
+  },
+  {
+    "id": "store.sql_channel_member_history.get_all.app_error",
+    "translation": "Failed to get records"
+  },
+  {
+    "id": "store.sql_channel_member_history.purge_history_before.app_error",
+    "translation": "Failed to purge records"
+  },
   {
     "id": "model.client.connecting.app_error",
     "translation": "We encountered an error while connecting to the server"
@@ -4878,6 +4942,30 @@
     "id": "model.config.is_valid.write_timeout.app_error",
     "translation": "Invalid value for write timeout."
   },
+  {
+    "id": "model.config.is_valid.message_export.enable.app_error",
+    "translation": "Message export job EnableExport setting must be either true or false"
+  },
+  {
+    "id": "model.config.is_valid.message_export.daily_runtime.app_error",
+    "translation": "Message export job DailyRuntime must be a 24-hour time stamp in the form HH:MM."
+  },
+  {
+    "id": "model.config.is_valid.message_export.export_from.app_error",
+    "translation": "Message export job ExportFromTimestamp must be a timestamp (expressed in seconds since unix epoch). Only messages sent after this timestamp will be exported."
+  },
+  {
+    "id": "model.config.is_valid.message_export.file_location.app_error",
+    "translation": "Message export job FileLocation must be a writable directory that export data will be written to"
+  },
+  {
+    "id": "model.config.is_valid.message_export.file_location.relative",
+    "translation": "Message export job FileLocation must be a sub-directory of FileSettings.Directory"
+  },
+  {
+    "id": "model.config.is_valid.message_export.batch_size.app_error",
+    "translation": "Message export job BatchSize must be a positive integer"
+  },
   {
     "id": "model.emoji.create_at.app_error",
     "translation": "Create at must be a valid time"
@@ -5474,6 +5562,10 @@
     "id": "store.sql.upgraded.warn",
     "translation": "The database schema has been upgraded to version %v"
   },
+  {
+    "id": "store.sql_compliance.message_export.app_error",
+    "translation": "Failed to select message export data"
+  },
   {
     "id": "store.sql_audit.get.finding.app_error",
     "translation": "We encountered an error finding the audits"