Ops: Add worker health to status page

[birkjernstrom]

We should add our worker to our public status page.

Challenge
Our worker is not accessible publicly, i.e cannot offer a health endpoint directly.

Solution

• Setup a scheduled task, e.g each minute, for the worker to store some checks in Redis.
• Add a /healthz endpoint to our public API checking the above and reporting 200 or 500 accordingly

[frankie567]

Discovered this:

• https://arq-docs.helpmanual.io/#health-checks
• https://github.com/python-arq/arq/blob/3914e48c530f0e5acf02cb340b1f8f3e201ba895/arq/worker.py#L891-L919

ARQ already writes its own healthcheck key in Redis; so maybe we just need to query for that key in our health endpoint.

[naineel1209]

Hi @birkjernstrom, I've created a PR with the changes mentioned in the discussions. Could you please check it?