add automation to submit PRs to update upon cosign releases

[bobcallaway]

Currently, when we have a new version of cosign, we need to manually update for our users:

• sigstore/cosign-installer
• sigstore/homebrew-tap
• bazel-contrib/rules_oci (see https://github.com/bazel-contrib/rules_oci/pull/82/files)
• actions/starter-workflows

It would be nice to have creation of a tag on the cosign repo trigger some automation that would automatically submit the correct PRs to the above list of repos.

Thoughts @cpanato?

[cpanato]

for sigstore/homebrew-tap we can add in the goreleaser

the other will require some automation but I think nothing is hard

i will work on that