This PR adds the ability for the LMS to publish `CERTIFICATE_REVOKED` events to the Event Bus. There is also work in progress for Credentials to consume these events.
[APER-2344]
We would like to start consuming Certificate related events in Credentials from the event bus. This PR starts the process by publishing CERTIFICATE_CREATED events to the event bus. It also introduces a new feature flag (`SEND_CERTIFICATE_CREATED_SIGNAL`) to gate the functionality.
* refactor: Merge the openedx certs app with lms one
Move the certs API from openedx into the lms certificates app.
Functionally, this is a no-op. Cleanup will happen in a subsequent
commit. This is simply a move.
