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/coding.go

@@ -160,8 +160,8 @@ func (c *Coding) TeamPerm(u *model.User, org string) (*model.Perm, error) {
 	return nil, nil
 }
 
-// Repo fetches the named repository from the remote system.
-func (c *Coding) Repo(ctx context.Context, u *model.User, owner, name string) (*model.Repo, error) {
+// Repo fetches the repository from the remote system.
+func (c *Coding) Repo(ctx context.Context, u *model.User, _ model.RemoteID, owner, name string) (*model.Repo, error) {
 	client := c.newClient(ctx, u)
 	project, err := client.GetProject(owner, name)
 	if err != nil {
@@ -172,6 +172,7 @@ func (c *Coding) Repo(ctx context.Context, u *model.User, owner, name string) (*
 		return nil, err
 	}
 	return &model.Repo{
+		// TODO(1138) RemoteID:     project.ID,
 		Owner:        project.Owner,
 		Name:         project.Name,
 		FullName:     projectFullName(project.Owner, project.Name),
@@ -199,6 +200,7 @@ func (c *Coding) Repos(ctx context.Context, u *model.User) ([]*model.Repo, error
 			return nil, err
 		}
 		repo := &model.Repo{
+			// TODO(1138) RemoteID:     project.ID,
 			Owner:        project.Owner,
 			Name:         project.Name,
 			FullName:     projectFullName(project.Owner, project.Name),