Release process: use github actions and release to bazel central registry

Discussed with @loosebazooka as part of adding a Bazel rule in this repo: we'd like the release process to:
- build the binaries for all platforms on GitHub Actions so it can be fully community-owned without a Google Cloud project required to use Cloud Build
- the Bazel rule wants to know the checksums of the binaries, currently I just mirrored the ones of the previous release in https://github.com/GoogleContainerTools/container-structure-test/blob/main/repositories.bzl#L5-L14
- the release should include an artifact which is a zip of this repo, so that Bazel users can fetch the rule without depending on GH to serve an artifact (might be forced to do this for the Bazel Central Registry, based on the outcome in https://github.com/bazelbuild/bazel-central-registry/pull/607)
- it should automagically publish to the Bazel Central Registry on each release using https://github.com/bazel-contrib/publish-to-bcr