Filter pods of interest

[consideRatio]

I planned adopting this on mybinder.org-deploy, but I realize that it can be a complicated. The namespace report should preferably then exclude all user pods and build pods, and perhaps even more to avoid being flooded with irrelevant noise.

So, the feature to develop, is something that makes us filter pods of interest somehow.

[consideRatio]

Ideas

• Ability to specify a label selector, which can involve statements like component notin (singleuser-server),app=jupyterhub
  Like we pass "--namespace={namespace}" now, we can also pass "--selector=${selector}". If it is blank, it won't affect anything.