Copy pasting a link to a card back while links attachment type is restricted does not show any UI warning

Issue Summary

This is reproducible on Data Center: (yes) / (no)

Steps to Reproduce

1. Create an Enterprise
2. Restrict the Link attachment type for an Enterprise
3. Go to the Enterprise belonging WS
4. Create a board with at least one list and a card on it
5. Open the card back
6. Copy paste the link to some external resource (for ex. giphy image: https://giphy.com/gifs/TempleOfGeek-doctor-who-10th-togdoctorwho-emVhwZ0cx7E2l125l9) to the card back

Expected Results

Link has not been pasted / attached to the card with a corresponding UI error message

Actual Results

Link has not been pasted / attached with no error message

Workaround

Not really a workaround, while other place where we could attach the link to the card back: open the card back and try to attach a link directly via the `Attachments` popup => `Link` field - error message appears on attempt to save the attachment.