feat: sync forks (#2364)

This allows syncing a branch of a fork with a branch of the base repo. It looks like this:
![grafik](/attachments/4508920c-7d0b-4330-9083-e3048733e38d)
This is only possible, if the fork don't have commits that are not in the main repo.

The feature is already working, but it is missing Finetuning, a better API, translations and tests, so this is currently WIP. It is also not tested with go-git.

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## Release notes
<!--URL:https://codeberg.org/forgejo/forgejo-->
- Features
  - [PR](https://codeberg.org/forgejo/forgejo/pulls/2364): <!--number 2364 --><!--line 0 --><!--description c3luYyBmb3Jrcw==-->sync forks<!--description-->
<!--end release-notes-assistant-->

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/2364
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: JakobDev <jakobdev@gmx.de>
Co-committed-by: JakobDev <jakobdev@gmx.de>

modules/git/commit.go

@@ -432,6 +432,11 @@ func (c *Commit) GetBranchName() (string, error) {
 	return strings.SplitN(strings.TrimSpace(data), "~", 2)[0], nil
 }
 
+// GetAllBranches returns a slice with all branches that contains this commit
+func (c *Commit) GetAllBranches() ([]string, error) {
+	return c.repo.getBranches(c, -1)
+}
+
 // CommitFileStatus represents status of files in a commit.
 type CommitFileStatus struct {
 	Added    []string