Add configuration and documentation for debugging remote instance in the cluster

[DiamondJoseph]

I needed to debug the contents of the authorization headers that are being passed into my tiled instance from the oauth2-proxy that it is deployed behind in the cluster: which requires that it is deployed with specific callback addresses that cannot easily be mocked from my machine.

While doing this, I thought I'd write up how to do it reliably, and make it configurable with minimal effort when I need need to look at what's going on in a running pod.

My scopes from oauth2 proxy are indeed not what I've requested, so my debugging narrowed down the problem.

Checklist

• Add a Changelog entry
• Add the ticket number which this PR closes to the comment section

[DiamondJoseph]

These duplicate the Dockerfile CMD arguments: Kubernetes uses command ~analogously to Docker ENTRYPOINT and args ~analogously to Docker CMD. Yes, it's frustrating.

Unfortunately if you set command, CMD args are ignored, if they were picked up we wouldn't need to duplicate this here.

[dylanmcreynolds]

I learned some new stuff from the PR. I don't absolutely love distributing debugpy with all instance of the tiled image, but it's better than trying to maintain dual images.