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/github/github_test.go

@@ -77,8 +77,9 @@ func Test_github(t *testing.T) {
 
 		g.Describe("Requesting a repository", func() {
 			g.It("Should return the repository details", func() {
-				repo, err := c.Repo(ctx, fakeUser, fakeRepo.Owner, fakeRepo.Name)
+				repo, err := c.Repo(ctx, fakeUser, fakeRepo.RemoteID, fakeRepo.Owner, fakeRepo.Name)
 				g.Assert(err).IsNil()
+				g.Assert(repo.RemoteID).Equal(fakeRepo.RemoteID)
 				g.Assert(repo.Owner).Equal(fakeRepo.Owner)
 				g.Assert(repo.Name).Equal(fakeRepo.Name)
 				g.Assert(repo.FullName).Equal(fakeRepo.FullName)
@@ -87,7 +88,7 @@ func Test_github(t *testing.T) {
 				g.Assert(repo.Link).Equal(fakeRepo.Link)
 			})
 			g.It("Should handle a not found error", func() {
-				_, err := c.Repo(ctx, fakeUser, fakeRepoNotFound.Owner, fakeRepoNotFound.Name)
+				_, err := c.Repo(ctx, fakeUser, "0", fakeRepoNotFound.Owner, fakeRepoNotFound.Name)
 				g.Assert(err).IsNotNil()
 			})
 		})
@@ -131,6 +132,7 @@ var (
 	}
 
 	fakeRepo = &model.Repo{
+		RemoteID:     "5",
 		Owner:        "octocat",
 		Name:         "Hello-World",
 		FullName:     "octocat/Hello-World",