Quick action for `unlinking` issues

As a follow-up to #214232 (closed), introduce the ability to unlink issues via quick actions.

Add new quick action /unlink <#issue> that destroys de link between the current issue and the provided one (despite the relation type).

This action will remove one link at a time, we have #393746 for adding support to remove multiple links.

Edited Jun 07, 2023 by Eugenia Grieff