Resolve#30917
Make the APIs for adding labels and replacing labels support both label
IDs and label names so the
[`actions/labeler`](https://github.com/actions/labeler) action can work
in Gitea.
<img width="600px"
src="https://github.com/go-gitea/gitea/assets/15528715/7835c771-f637-4c57-9ce5-e4fbf56fa0d3"
/>
(cherry picked from commit b3beaed147466739de0c24fd80206b5af8b71617)
Conflicts:
- modules/structs/issue_label.go
Resolved by applying the Gitea change by hand.
- tests/integration/api_issue_label_test.go
Resolved by copying the new tests.
