Allow to delete UserAchievements

Originally started as a Discord conversation by @leetickett-gitlab: https://canary.discord.com/channels/778180511088640070/997442331202564176/1116751538573029376

I think we should create a userAchievementDelete mutation. I can see there being instances where we don't want award/revoke For example if I make a mistake and issue a core team member achievment to someone twice. I don't really want to see the trail of one being revoked

Deleting the UserAchievement should be locked to the owner role. Maintainers can only revoke.