* 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