Add patch release notes and docs fixes

[coruscating]

Summary

Closes #1401. Our release notes currently doesn't include notes of the patch releases before the most recent minor release. This PR updates release_notes.rst to build previous patch releases (0.3.1 isn't rendering but I think it's too old to be useful now anyways). The new process prior to release is that release notes from the most recent minor version's patch releases should be deleted from the main branch prior to a new minor release, and release_notes.rst needs to have a new directive added for the previous stable branch.

Details and comments

A few other minor changes:

• Wraps the output text of jupyter-sphinx blocks
• Update the contributor guide to include release note subcategories
• Suppress the debugger warning during the docs build by setting PYDEVD_DISABLE_FILE_VALIDATION=1
• Add a link to the main branch to the dev docs banner

[coruscating]

I just noticed the notes in the github build only goes back to the 0.4 prelude, which I didn't catch because my local build went back to 0.2: https://qiskit-extensions.github.io/qiskit-experiments/dev/release_notes.html. In the logs, reno only saw 0.5.x and 0.4 in stable/0.5, maybe because it doesn't know about the older tags? I suppose we may as well put in a PR to backfill the old notes manually since we want to do that anyways.