Enable Changesets

[remcohaszing]

Changesets replaces lerna-lite. Releases are made using the release workflow. The changeset configuration is based on Astro and MDX analyzer.

Each package now has a prepack script. This is run before creating an npm package, including by Changesets.

Also npm provenance was enabled.

This requires an npm CI token to be set as the NPM_TOKEN GitHub actions secret.