Separate notes archive to non-toctree pages

- Having notes archive in the main toctree led to a very long link,
  which caused a messed up PDF build.
- But also maybe the notes archive shouldn't be in the PDF build which
  would be archived on Zenodo.
- This makes a stub notes-archive page, which links (non-toctree)
  links to the notes archive page (which still gets buildt, but not in
  the toctree, which means not on the left sidebar)
- The primary effect is that the archive from the 2024 workshop isn't
  included in the PDF or singlehtml builds.  Which is probably how it
  should be anyway.  A secondary effect is that there isn't a left
  sidebar link directly to the 2024 notes (but there is to the page
  that links them).

Review:

- Confirm it's not in pdf or singlehtml
- Confirm that this is the right choice to make for where it should be
  visible.
- Consider if the notes should be in a zenodo-archived git repo at all
  (since the repo itself will be archived, right?).  I think it's
  probably OK and consistent with the licenses we had said it would be
  realesed under - right?