Bump base image to Ubuntu 24.04 LTS

[yuvipanda]

Moves from 22.04 to 24.04

[yuvipanda]

@manics thoughts on rolling this into the release?

[weiji14]

Couple of comments:

1. Do we need to handle https://github.com/jupyterhub/repo2docker/issues/1346 somehow? E.g. by overriding the default 'ubuntu' user with 'jovyan'? Or is that for downstream repos to handle?
2. There are still a few references to 'Jammy Jellyfish (22.04)' in the repo (e.g. from this search), might need to update them to 'Noble Numbat (24.04)'.

[yuvipanda]

Do we need to handle https://github.com/jupyterhub/repo2docker/issues/1346 somehow?

This feels critical to test, as our new user jovyan may now have uid 1001 instead of the 1000 it used to, causing a lot of havoc in places.

[minrk]

From discussion: we are going to hold this one until after we can cut a release, then deal with it.

My inclination is to make sure we keep using id 1000 by clobbering the existing ubuntu user, rather than trying to figure out the consequences of changing the default uid.

[yuvipanda]

Clobber clobber clobber

[manics]

https://github.com/manics/repo2docker/commit/5c5656b087592e8f305a74a28f6efd65e7a7f437 renames/moves the existing user and group if found. Cherry-pick it if you're happy with it. We should probably add a test too.