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

templates/globalrelay_compliance_export_message.html

@@ -0,0 +1,8 @@
+{{define "globalrelay_compliance_export_message"}}
+<li class="message">
+    <span class="sent_time">{{.Props.SentTime}}</span>
+    <span class="username">@{{.Props.Username}}</span>
+    <span class="email">({{.Props.Email}}):</span>
+    <span class="message">{{.Props.Message}}</span>
+</li>
+{{end}}