[BUG] Implement commit mail selection for other Git operations

- Implement the commit mail selection feature for the other supported
Git operations that can be done trough the web UI.
- Adds integration tests (goodluck reviewing this).
- Ref: #1788

Co-authored-by: 0ko <0ko@noreply.codeberg.org>

tests/integration/repo_mergecommit_revert_test.go

@@ -26,6 +26,7 @@ func TestRepoMergeCommitRevert(t *testing.T) {
 		"commit_message":  "test message",
 		"commit_choice":   "direct",
 		"new_branch_name": "test-revert-branch-1",
+		"commit_mail_id":  "-1",
 	})
 	resp = session.MakeRequest(t, req, http.StatusSeeOther)