Tidy up repo

[lcian]

• Revisit README.md and such instructions so that it's easy for people to add new conventions and generally work with the repo
• Add a .envrc to make this even easier
• Revisit scripts
• Move all generated stuff to a generated directory
• Update release and CI stuff accordingly
• Enforce changelog (?)
• Either using weaver or not, use Jinja templates or something more readable and maintainable for the codegen
• Split lint and lint-fix everywhere
• Run codegen and lint and fix in GH

[linear]

CON-62 Tidy up repo