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/notification_push.go

@@ -79,11 +79,11 @@ func (a *App) sendPushNotificationSync(post *model.Post, user *model.User, chann
 		msg.ChannelName = channelName
 	}
 
-	if ou, ok := post.Props["override_username"].(string); ok && cfg.ServiceSettings.EnablePostUsernameOverride {
+	if ou, ok := post.Props["override_username"].(string); ok && *cfg.ServiceSettings.EnablePostUsernameOverride {
 		msg.OverrideUsername = ou
 	}
 
-	if oi, ok := post.Props["override_icon_url"].(string); ok && cfg.ServiceSettings.EnablePostIconOverride {
+	if oi, ok := post.Props["override_icon_url"].(string); ok && *cfg.ServiceSettings.EnablePostIconOverride {
 		msg.OverrideIconUrl = oi
 	}
 
@@ -130,7 +130,7 @@ func (a *App) sendPushNotification(notification *postNotification, user *model.U
 	}
 
 	channelName := notification.GetChannelName(nameFormat, user.Id)
-	senderName := notification.GetSenderName(nameFormat, cfg.ServiceSettings.EnablePostUsernameOverride)
+	senderName := notification.GetSenderName(nameFormat, *cfg.ServiceSettings.EnablePostUsernameOverride)
 
 	c := a.Srv.PushNotificationsHub.GetGoChannelFromUserId(user.Id)
 	c <- PushNotification{