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

app/command.go

@@ -394,7 +394,7 @@ func (a *App) HandleCommandResponsePost(command *model.Command, args *model.Comm
 
 	isBotPost := !builtIn
 
-	if a.Config().ServiceSettings.EnablePostUsernameOverride {
+	if *a.Config().ServiceSettings.EnablePostUsernameOverride {
 		if len(command.Username) != 0 {
 			post.AddProp("override_username", command.Username)
 			isBotPost = true
@@ -404,7 +404,7 @@ func (a *App) HandleCommandResponsePost(command *model.Command, args *model.Comm
 		}
 	}
 
-	if a.Config().ServiceSettings.EnablePostIconOverride {
+	if *a.Config().ServiceSettings.EnablePostIconOverride {
 		if len(command.IconURL) != 0 {
 			post.AddProp("override_icon_url", command.IconURL)
 			isBotPost = true