Alternative to https://github.com/go-gitea/gitea/pull/27439. Removes a few spammy labels, and disables `sync-labels` which make it never remove labels (which is default behaviour).
Implements https://github.com/GiteaBot/gitea-backporter/issues/93 using [`actions/labeler`](https://github.com/actions/labeler). Very basic configuration, can be extended later.