Send message in channel when locking via API

[RaniSputnik]

When I lock via the API, I would like to see a message posted in the channel to indicate I've locked a resource. At the moment this just happens with no visibility to other users.

[connorads]

Not ideal but in the meantime users can use /locks to see what is currently locked, including when locked via the API

[connorads]

If a team has fully integrated their CI pipeline with Lockbot they might not actually want to be notified so this behaviour should be configurable.