[API] Add affected files of commits to commit struct (#14579)

[API] Add affected files of commits to commit struct (#14579)

* Add files affected by a commit to gitea API -- similar to github

* Add files affected by a commit to gitea API

* Fix stupid error

* Fix other stupid typo

* Generate swagger tmpl

* Comply with convert to git commit refacto

* update swagger docs

* extend test

* format code

* Update integrations/api_repo_git_commits_test.go

* Update modules/convert/git_commit.go

Co-authored-by: Laurent Cahour <laurent.cahour@dont-nod.com>
Co-authored-by: zeripath <art27@cantab.net>