WIP: Allow BinderHub to work with an existing JupyterHub

[manics]

I thought this used to be possible, but it might be my imagination.

https://discourse.jupyter.org/t/installing-binderhub-to-existing-jupyterhub/26561

[yuvipanda]

I was just talking to @minrk about this this moning! What I'd like to propose is that we make https://github.com/2i2c-org/binderhub-service/ the official chart for binderhub (merge that repo into this repo), and deprecate the existing chart. This keeps the clean split between binderhub and jupyterhub, and allows the binderhub setup to be used with alternative frontends more easily as well (like https://github.com/yuvipanda/jupyterhub-fancy-profiles).

We (2i2c) have now been able to deploy many mybinder.org style binderhubs with that chart now (with docs at https://infrastructure.2i2c.org/howto/features/binderhub-ui/).

The plan as I had talked about with @minrk is to first migrate https://github.com/jupyterhub/mybinder.org-deploy to use binderhub-service, to iron out any issues that may exist. And then merge that in here afterwards. I'd also like 2i2c-org/binderhub-service#57 to be implemented before that.

What do you think of that, @manics?

[manics]

@yuvipanda Sounds good to me! Do you mind opening a new issue in this repo, then we can close this and direct people there. We can also use the issue to discuss the layout of this repo, e.g. should the chart remain part of this repo or not.