[TC][Admin/Partners page] [Functionality] Admin is able to add a link to the partner's social media in the field "Посилання". A mandatory field, symbols limit is 255.

**Priority: Medium**

**Preconditions**
1. Go to the site - https://frontend.historycode.online/admin-panel.
2. Login as admin.
3. Go to the block "Admin/Партнери".
4. Open the modal window "Додати партнера" by pressing the button "Створити партнера".
5. Was entered the text in the field "Назва" and was added the image to field "Лого"
6. Was clicked the button "Додати соціальну мережу".
7. From dropdown list "Соціальна мережа" was chosen the social network.

**Steps to reproduce**
1. Try to add 256 symbols to the "Посилання" field.

**Expected result**
The system doesn't allow adding 256st symbol and displays a counter set at 255 symbols.

**[User Story #1491](https://github.com/ita-social-projects/StreetCode/issues/1491)**

**Related bug:**