Refactor rename user and rename organization (#24052)

This PR is a refactor at the beginning. And now it did 4 things.
- [x] Move renaming organizaiton and user logics into services layer and
merged as one function
- [x] Support rename a user capitalization only. For example, rename the
user from `Lunny` to `lunny`. We just need to change one table `user`
and others should not be touched.
- [x] Before this PR, some renaming were missed like `agit`
- [x] Fix bug the API reutrned from `http.StatusNoContent` to `http.StatusOK`

tests/integration/api_admin_test.go

@@ -241,3 +241,44 @@ func TestAPICreateRepoForUser(t *testing.T) {
 	)
 	MakeRequest(t, req, http.StatusCreated)
 }
+
+func TestAPIRenameUser(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+	adminUsername := "user1"
+	token := getUserToken(t, adminUsername, auth_model.AccessTokenScopeSudo)
+	urlStr := fmt.Sprintf("/api/v1/admin/users/%s/rename?token=%s", "user2", token)
+	req := NewRequestWithValues(t, "POST", urlStr, map[string]string{
+		// required
+		"new_name": "User2",
+	})
+	MakeRequest(t, req, http.StatusOK)
+
+	urlStr = fmt.Sprintf("/api/v1/admin/users/%s/rename?token=%s", "User2", token)
+	req = NewRequestWithValues(t, "POST", urlStr, map[string]string{
+		// required
+		"new_name": "User2-2-2",
+	})
+	MakeRequest(t, req, http.StatusOK)
+
+	urlStr = fmt.Sprintf("/api/v1/admin/users/%s/rename?token=%s", "User2", token)
+	req = NewRequestWithValues(t, "POST", urlStr, map[string]string{
+		// required
+		"new_name": "user1",
+	})
+	// the old user name still be used by with a redirect
+	MakeRequest(t, req, http.StatusTemporaryRedirect)
+
+	urlStr = fmt.Sprintf("/api/v1/admin/users/%s/rename?token=%s", "User2-2-2", token)
+	req = NewRequestWithValues(t, "POST", urlStr, map[string]string{
+		// required
+		"new_name": "user1",
+	})
+	MakeRequest(t, req, http.StatusUnprocessableEntity)
+
+	urlStr = fmt.Sprintf("/api/v1/admin/users/%s/rename?token=%s", "User2-2-2", token)
+	req = NewRequestWithValues(t, "POST", urlStr, map[string]string{
+		// required
+		"new_name": "user2",
+	})
+	MakeRequest(t, req, http.StatusOK)
+}