AAP-47956 Use pg_notify for cancel and debugging, abandon socket approach

[AlanCoding]

SUMMARY

The main reason we didn't do this before was that we didn't have a means of splitting messages into multi-part messages to get under the 8,000 character limit of pg_notify. This is addressed with https://github.com/ansible/dispatcherd/pull/191 which I think is fairly final & durable.

Additionally, eda-server is making fast progress, and I want to push for us both to have the same solution, and the sockfile just takes too much debugging for it to be worth it.

We might add back in the socket broker later, or we might just have some sort of custom task on shutdown where we force it to dump the status output to logs or a file. If the self-check messages are, at all, working, this will probably cover us.

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API