* FEATURE: Trigger webhook when assigning and unassigning topics
This PR creates a custom webhook event that you can now select when
creating a webhook to trigger only when a topic has been assigned or
unassigned.
* removed unused file
* Removed functionality that was added to core
This PR into discourse core:
https://github.com/discourse/discourse/pull/9110
adds what was removed in this commit.
It is better to have this logic in core so that it is discoverable and
future webhooks won't end up accidentally using the same ID.
Rafael dos Santos Silva
Blake Erickson