Add release-plz workflow

This adds the release-plz CI using their [basic, recommended workflow yaml](https://release-plz.dev/docs/github/quickstart#3-setup-the-workflow) as a solution to https://github.com/entropyxyz/devops-infrastructure/issues/133. I would like to iterate on this by creating a release-plz bot app and use that for our github token in the CI (see the [documented recommendation](https://release-plz.dev/docs/github/token#use-a-github-app)), but I don't think this is necessary for this first version and can follow up with a future PR.