System Console: Email notification content setting (#7122)

* PLT-7195: Added new config option, new license feature, and config UI to system console. Still need to implement behaviour change in email batching code

* PLT-7195: Modified batch emails to respect email notification content type setting

* PLT-7195: Tweaking the colours a bit

* PLT-7195: Added support for email notification content type setting in immediate (non-batched) notification messages. Attempted to clean up the code somewhat. Unit tests coming in a future commit

* PLT-7195: Added unit tests for non-batched emails

* Checked license when applying email content settings

* Changed return type of getFormattedPostTime

webapp/i18n/en.json

@@ -350,6 +350,11 @@
   "admin.email.enableSMTPAuthTitle": "Enable SMTP Authentication:",
   "admin.email.enableSMTPAuthDesc": "When enabled, username and password are used for authenticating to the SMTP server.",
   "admin.email.testing": "Testing...",
+  "admin.email.notification.contents.full": "Send full message contents",
+  "admin.email.notification.contents.generic": "Send generic description with only sender name",
+  "admin.email.notification.contents.title": "Email Notification Contents: ",
+  "admin.email.notification.contents.full.description": "Sender name and channel are included in email notifications.</br>Typically used for compliance reasons if Mattermost contains confidential information and policy dictates it cannot be stored in email.",
+  "admin.email.notification.contents.generic.description": "Only the name of the person who sent the message, with no information about channel name or message contents are included in email notifications.</br>Typically used for compliance reasons if Mattermost contains confidential information and policy dictates it cannot be stored in email.",
   "admin.false": "false",
   "admin.file.enableFileAttachments": "Allow File Sharing:",
   "admin.file.enableFileAttachmentsDesc": "When false, disables file sharing on the server. All file and image uploads on messages are forbidden across clients and devices, including mobile.",