Fetch repositories with remote ID if possible (#1078)

Use IDs of the forge to fetch repositories instead of their names and owner names. This improves handling of renamed and transferred repos.

TODO

- [ ] try to support as many forges as possible
    - [x] Gogs (no API)
    - [ ] Bitbucket Server
    - [x] Coding (no API?)
- [x] update repo every time it is fetched or received from the forge
- [x] if repo remote IDs are not available, use owner / name to get it
- [x] handle redirections (redirect a renamed repo to its new path)
- [x] ~~pull all repos once during migration to update ID (?)~~ issue fixed by on-demand loading of remote IDs
- [x] handle redirections in web UI
- [ ] improve handling of hooks after a repo was renamed (currently it checks for a redirection to the repo)
- [x] tests
- [x] `UNIQUE` constraint for remote IDs after migration shouldn't work (all repos have an empty string as remote ID)

close #854
close #648 partial
close https://codeberg.org/Codeberg-CI/feedback/issues/46

Possible follow-up PRs
- apply the same scheme on everything fetched from the remote (currently only users)

Co-authored-by: 6543 <6543@obermui.de>

server/remote/coding/hook.go

@@ -137,6 +137,7 @@ func convertRepository(repo *Repository) (*model.Repo, error) {
 	}
 
 	return &model.Repo{
+		// TODO RemoteID: repo.ID,
 		Owner:    matches[1],
 		Name:     repo.Name,
 		FullName: projectFullName(repo.Owner.GlobalKey, repo.Name),