Add option to set worker healthcheck timeout

[mmac-m3a]

Summary

Adding new command line and config option worker_healthcheck_timeout which sets the timeout for worker liveness from the supervisor when multiple workers are in use. Default timeout is unchanged as well as frequency of health checks.

Rationale

Applications with CPU intensive synchronous startup may starve the worker process for CPU cycles and make the pong thread generate response too late, which in turn makes the supervisor kill and relaunch the worker.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

Rationale for no explicit test

I was not able to create simple unit test that would reliably trigger the health check timeout. I can 100% reliably trigger it in my application and I've also verified that longer health check timeout resolves the problem.