MM-9728: Online migration for advanced permissions phase 2 (#8744)

* MM-9728: Online migration for advanced permissions phase 2

* Add unit tests for new store functions.

* Move migration specific code to own file.

* Add migration state function test.

* Style fixes.

* Add i18n strings.

* Fix mocks.

* Add TestMain to migrations package tests.

* Fix typo.

* Fix review comments.

* Fix up the "Check if migration is done" check to actually work.

model/job.go

@@ -16,6 +16,7 @@ const (
 	JOB_TYPE_ELASTICSEARCH_POST_INDEXING    = "elasticsearch_post_indexing"
 	JOB_TYPE_ELASTICSEARCH_POST_AGGREGATION = "elasticsearch_post_aggregation"
 	JOB_TYPE_LDAP_SYNC                      = "ldap_sync"
+	JOB_TYPE_MIGRATIONS                     = "migrations"
 
 	JOB_STATUS_PENDING          = "pending"
 	JOB_STATUS_IN_PROGRESS      = "in_progress"
@@ -52,6 +53,7 @@ func (j *Job) IsValid() *AppError {
 	case JOB_TYPE_ELASTICSEARCH_POST_AGGREGATION:
 	case JOB_TYPE_LDAP_SYNC:
 	case JOB_TYPE_MESSAGE_EXPORT:
+	case JOB_TYPE_MIGRATIONS:
 	default:
 		return NewAppError("Job.IsValid", "model.job.is_valid.type.app_error", nil, "id="+j.Id, http.StatusBadRequest)
 	}

model/migration.go

@@ -0,0 +1,8 @@
+// Copyright (c) 2018-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+const (
+	MIGRATION_KEY_ADVANCED_PERMISSIONS_PHASE_2 = "migration_advanced_permissions_phase_2"
+)