Add releaser workflows to the repo

[jtpio]

Add releaser workflows to be able to release from the repo directly with the bot account: https://github.com/jupyterlite-bot

• Follow setup from https://jupyter-releaser.readthedocs.io/en/latest/how_to_guides/convert_repo_from_repo.html
• Add ADMIN_GITHUB_TOKEN to the repo secrets
• Add PYPI_TOKEN to the repo secrets
• Add NPM_TOKEN to the repo secrets
• Update RELEASE.md

The bot has been added to the repo:

[jtpio]

I tested this setup with jupyterlite-p5-kernel and it appears to be working: https://github.com/jupyterlite/p5-kernel/releases/tag/v0.1.1

[jtpio]

Happy to make the next release just to make sure it works well.

[martinRenou]

Thanks!