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/config_test.go

@@ -51,7 +51,7 @@ func TestConfigListener(t *testing.T) {
 
 	originalSiteName := th.App.Config().TeamSettings.SiteName
 	th.App.UpdateConfig(func(cfg *model.Config) {
-		cfg.TeamSettings.SiteName = "test123"
+		*cfg.TeamSettings.SiteName = "test123"
 	})
 
 	listenerCalled := false
@@ -60,9 +60,9 @@ func TestConfigListener(t *testing.T) {
 			t.Fatal("listener called twice")
 		}
 
-		if oldConfig.TeamSettings.SiteName != "test123" {
+		if *oldConfig.TeamSettings.SiteName != "test123" {
 			t.Fatal("old config contains incorrect site name")
-		} else if newConfig.TeamSettings.SiteName != originalSiteName {
+		} else if *newConfig.TeamSettings.SiteName != *originalSiteName {
 			t.Fatal("new config contains incorrect site name")
 		}