MM-60115, MM-62436, MM-62493: Compliance export downloads from local and s3; e2e tests (#29806)

* add ZipReader method to filestore and file/s3 backends

to merge

to merge

* add WriteStreamResponse as an alternative to WriteFileResponse

* add generated layers

* enable download link; download job endpoint now streams export dir zips

* fix MM-62493

* re-enable e2e tests--we have download links, folks

* Add tests for ZipReader in filestore and s3store

* remove unnecessary error return on ZipReader

* little cleanup

* improve tests; some refactoring: s.Nil(err) -> s.NoError(err)

* blank commit

* backwards compatability for pre-10.5 job downloads

* compress file response; better errors; better comments; PR comments

* update generated app layers

* improve/widen tests; improve comments; simplify localstore ZipReader

* regenerate layers

* follow GoDoc conventions

* update generated layers

* remove unnecessary comment

* in jobs/job-id/download, clean exportDir before sending to ZipReader

* better comments; add an error return on ZipReader

* improve file permissions

* adjust tests for new error returns

* linting

* i18n

server/enterprise/message_export/shared/shared.go

@@ -21,7 +21,8 @@ import (
 )
 
 const (
-	MissingFileMessage = "File missing for post; cannot copy file to archive"
+	MissingFileMessageDuringBackendRead = "File backend read: File missing for post; cannot copy file to archive"
+	MissingFileMessageDuringCopy        = "Copy buffer: File missing for post; cannot copy file to archive"
 
 	EstimatedPostCount = 10_000_000