Add admins to carbonplan hub

[choldgraf]

I tried to mimic how this is done on the OpenScapes hub

closes #566

[yuvipanda]

Let's do it like https://github.com/2i2c-org/pilot-hubs/blob/151faa89e92d7ca596a31bbe9e58e16de758a2f7/config/hubs/2i2c.cluster.yaml#L50 instead? That'll mean only the listed users can log in (right now anyone with GitHub can login lol), and they can add more users in the admin panel when they need to log in.

[yuvipanda]

Also #558 is needed to deploy to the new carbonplan hub

[choldgraf]

ok I think this is what you mean? Do we also need to do this in the openscapes hub? https://github.com/2i2c-org/pilot-hubs/blob/151faa89e92d7ca596a31bbe9e58e16de758a2f7/config/hubs/openscapes.cluster.yaml

We should document this in the pilot hubs docs (maybe we should rename that to "Hub Engineer Handbook/guide/etc"?)

[yuvipanda]

Yep! I think we should do this for openscapes (and all our hubs really), since otherwise anyone with a github login can get in.

The * and & are YAML anchors that need to be unique within the document, so they were <hubname>_users in 2i2c.clusters.yaml. Not the case here though.

There's docs on adding new users in https://pilot.2i2c.org/en/latest/admin/howto/manage-users.html, but we should have equivalent in the '2i2c engineer handbook'