Add `dev` flag to qhub CLI

[iameskild]

This is a follow up from a discussion that @costrouc, @tonyfast, @viniciusdc and I had a few weeks ago.

During the qhub development and testing process, developers often relying on little "tricks" in order to work on or test particular sections of the code. At this point, we have accrued a decent amount of "tech debt" with all of these little "tricks", see qhub/utils.py. Here is a list a few annoyances that this dev flag might address:

• setting the qhub_version in the qhub-config.yaml to version used during development or to some other desired version
  • currently relying exporting QHUB_GH_BRANCH to set this version
• setting the docker image tags to some desired version
  • currently relying exporting QHUB_GH_BRANCH to set these tags
• setting the qhub-dask to some desired version
  • currently handled manually
• setting the kubernetes version to some desired version
  • currently relying on QHUB_K8S_VERSION
• for the gitops workflow, it would be nice to preset the version of qhub or branch of qhub to install from
  • currently relying exporting QHUB_GH_BRANCH to set this branch

These are just a few of the things that can be handled with a dev flag.

[costrouc]

I agree having a feature like this would be useful and help to separate development based additions to qhub.

[trallard]

@iameskild I believe this was now added in the new CLI, do we need to keep this open?

[iameskild]

@trallard the associated PR is still open but I just linked the two :)