Add release notes for Ubuntu 23.04 "Lunar Lobster"

[Hyask]

Context

Along the past 20 years, Ubuntu release notes have been published in various places: emails, wiki, Discourse...
Now that we have one single place to store them all, let's go back in history and save them all here.

This issue is for tracking the work for integrating the Ubuntu 23.04 "Lunar Lobster" release note to this repo.

Instructions for the pull-request

• The first commit should import the original document as-is, without any syntax fix.
• Any number of subsequent commits will fix the syntax until the document renders correctly.
• The link to the original document will be provided (for ease of review and archiving/historical purpose):
  • In the first commit log importing it.
  • Also at the top of the final document in a comment: <!-- Originally published here: <link> -->.

Acceptance criteria

• The release notes for Ubuntu 23.04 "Lunar Lobster" have been found.
• It has been migrated to a corresponding folder in ./docs.
• Its syntax has been updated to work with this repo's build system (Sphinx).
• An entry has been added in the table of content in ./docs/archive.md.
• No need to also import the release schedule (although not blocking if you do, and if you find it, please include the link).
• A corresponding pull-request has been opened, reviewed and merged, following the instructions above.