chore: create a release workflow

[nirinchev]

This PR adds the following:

1. A "Prepare Release" workflow that can be invoked with an update type (patch/minor/major). Once run, it will bump the package version, create a release/version branch, and open a PR.
2. A package job for the PR workflow. This is run only on release/* branches and will run npm pack and archive the output.
3. A "Publish Release" workflow that needs to be manually invoked. It will run npm publish, merge the release PR, then create a github release with an autogenerated changelog. This workflow needs to access the npm token as an environment secret and as such needs an approval from a member of the devtools team to run (who is not the person who ran the workflow).

I'm working with IT on getting the actual token, so this wouldn't work until we get it.

[addaleax]

Nice, let's try this out!