Set up new repo for data analysis

[alexdewar]

As discussed with @tsmbland and @dalonsoa, the plan is to include a Jupyter notebook (or two) in the main repo for our own analyses while we're developing. Longer term, however, it makes sense for these notebooks to live in a separate repo, partly so that it can evolve separately (it doesn't need to be tied to the MUSE2 release schedule) and partly because all the tooling will be different (and Python-based).

This should be set up with all our usual Python tooling (perhaps with uv for dependency management?). Initially it will be a bit of a dumping ground for things -- but I think that's ok! It's just handy to have scripts and example notebooks in one place. Maybe one day we'll have something that we'll want to tidy it up and publish on PyPI, but for now I think it'll just be useful to have some examples largely for our own use.

This new repo could have its own documentation (it seems there's an mkdocs plugin to include notebooks). We should also signpost it from the main MUSE2 documentation.