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/system.go

@@ -456,7 +456,7 @@ func testS3(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if cfg.FileSettings.AmazonS3SecretAccessKey == model.FAKE_SETTING {
+	if *cfg.FileSettings.AmazonS3SecretAccessKey == model.FAKE_SETTING {
 		cfg.FileSettings.AmazonS3SecretAccessKey = c.App.Config().FileSettings.AmazonS3SecretAccessKey
 	}