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

model/config_test.go

@@ -59,7 +59,7 @@ func TestConfigDefaultFileSettingsDirectory(t *testing.T) {
 	c1 := Config{}
 	c1.SetDefaults()
 
-	if c1.FileSettings.Directory != "./data/" {
+	if *c1.FileSettings.Directory != "./data/" {
 		t.Fatal("FileSettings.Directory should default to './data/'")
 	}
 }