[API][Admin/Editor/Positions] Verify if the position with invalid data (> 50 characters) can be created using POST method

**Priority:**
High

**Preconditions**
1.Postman is opened
2.User is authorized as admin
3.The POST method is chosen

**Steps to reproduce**
1. Input a valid endpoint https://backend.historycode.online/api/Position/Create.
2. Add the required data in invalid format (52characters) to the body:
{
"position": "string"
}
(e.g. "position": "qaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqaqa")
3. Click the ''Send'' button.

**Expected result**
1. Status 400 - Bad request.
2. The error message is appeared: "Максимальна довжина поля 'Позиція' - 50''

**User story:**#833