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

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