XYZ-35: Added Support for GlobalRelay Compliance Export Format

* Added username to ChannelMemberHistory struct in anticipation of supporting GlobalRelay in Compliance Export
* Removed translation from debug output - this makes it complicated to use utils functions from tests in the enterprise repo
* Added an advanced email function that allows for greater control over message details. Updated MessageExport config to support GlobalRelay. Added attachment support to InBucket unit tests
* Moving templates in from enterprise to solve test issues
* Added export format to diagnostics
* Changed email attachment code to use FileBackend so that S3 storage is properly supported

store/sqlstore/compliance_store.go

@@ -225,7 +225,8 @@ func (s SqlComplianceStore) MessageExport(after int64, limit int) store.StoreCha
 				Channels.Id AS ChannelId,
 				Channels.DisplayName AS ChannelDisplayName,
 				Users.Id AS UserId,
-				Users.Email AS UserEmail
+				Users.Email AS UserEmail,
+				Users.Username
 			FROM
 				Posts
 				LEFT OUTER JOIN Channels ON Posts.ChannelId = Channels.Id