[GITEA] Allow user to select email for file operations in Web UI

- Add a dropdown to the web interface for changing files to select which
Email should be used for the commit. It only shows (and verifies) that a
activated mail can be used, while this isn't necessary, it's better to
have this already in place.
- Added integration testing.
- Resolves https://codeberg.org/forgejo/forgejo/issues/281

(cherry picked from commit 564e701f40)
(cherry picked from commit de8f2e03cc)
(cherry picked from commit 0182cff12e)

tests/integration/empty_repo_test.go

@@ -55,10 +55,11 @@ func TestEmptyRepoAddFile(t *testing.T) {
 	doc := NewHTMLParser(t, resp.Body).Find(`input[name="commit_choice"]`)
 	assert.Empty(t, doc.AttrOr("checked", "_no_"))
 	req = NewRequestWithValues(t, "POST", "/user30/empty/_new/"+setting.Repository.DefaultBranch, map[string]string{
-		"_csrf":         GetCSRF(t, session, "/user/settings"),
-		"commit_choice": "direct",
-		"tree_path":     "test-file.md",
-		"content":       "newly-added-test-file",
+		"_csrf":          GetCSRF(t, session, "/user/settings"),
+		"commit_choice":  "direct",
+		"tree_path":      "test-file.md",
+		"content":        "newly-added-test-file",
+		"commit_mail_id": "32",
 	})
 
 	resp = session.MakeRequest(t, req, http.StatusSeeOther)