UserStore migration (#15563)

* Migration completed

* Fix tests

* Fix tests

* Fix tests

* Suggestions

* Trigger CI

* Suggestions

* Merge with master

* Trigger CI

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Agniva De Sarker <agnivade@yahoo.co.in>

app/config.go

@@ -247,9 +247,9 @@ func (s *Server) ensureInstallationDate() error {
 		return nil
 	}
 
-	installDate, appErr := s.Store.User().InferSystemInstallDate()
+	installDate, nErr := s.Store.User().InferSystemInstallDate()
 	var installationDate int64
-	if appErr == nil && installDate > 0 {
+	if nErr == nil && installDate > 0 {
 		installationDate = installDate
 	} else {
 		installationDate = utils.MillisFromTime(time.Now())