MM-10658 Change config fields to pointers (#9033)

* MM 10658 Change config fields to pointers (#8898)

* Change fields of config structs to pointers and set defaults

MM-10658 https://github.com/mattermost/mattermost-server/issues/8841

* Fix tests that go broken during switching config structs to pointers

MM-10658 https://github.com/mattermost/mattermost-server/issues/8841

* Apply changes of current master while switching config structs to pointers

MM-10658 https://github.com/mattermost/mattermost-server/issues/8841

* Fix new config pointer uses

* Fix app tests

* Fix mail test

* remove debugging statement

* fix TestUpdateConfig

* assign config consistently

* initialize AmazonS3Region in TestS3TestConnection

* initialize fields for TestEmailTest

* fix TestCheckMandatoryS3Fields

api4/team_test.go

@@ -1952,7 +1952,7 @@ func TestInviteUsersToTeam(t *testing.T) {
 		}
 	}
 
-	th.App.UpdateConfig(func(cfg *model.Config) { cfg.TeamSettings.RestrictCreationToDomains = "@global.com,@common.com" })
+	th.App.UpdateConfig(func(cfg *model.Config) { *cfg.TeamSettings.RestrictCreationToDomains = "@global.com,@common.com" })
 
 	t.Run("restricted domains", func(t *testing.T) {
 		err := th.App.InviteNewUsersToTeam(emailList, th.BasicTeam.Id, th.BasicUser.Id)