fix(admin): the setting of a federation attribute for some application form item
Created by: HejdaJakub
- The setting of a federation attribute used to be broken - user wasn't able to change the federation attribute via dialog.
- In this PR was also fixed the setting of a custom federation attribute.
- In this PR was also added a check which disables to add a required item which is hidden or disabled (uneditable) and also has no source or federation attribute (it can't have any prefilled value).