Auto create PR to upstream OLM repo when a new release is cut

[NissesSenap]

Is your feature request related to a problem? Please describe. As a part of https://github.com/grafana-operator/grafana-operator/pull/1234 we won't no longer check in the tag in the bundle/manifests. Instead, we will just set the image digest in the upstream OLM repos.

Since everything is disconnected from each other, we can now automate a PR to the OLM repos when the image has been generated.

Describe the solution you'd like

• Create a github actions that runs after the container image has been published.
• clone this repo, update the digest by running the needed command.
• Create a PR to the OLM repos.
• Tag the maintainers in the PR and when all checks pass we can perform a merge command.

Describe alternatives you've considered Keep on doing it manually.

[NissesSenap]

To not generate a bunch of PRs to the upstream OLM repos, work on this repo should start in a public repo that the PR creator owns. This way we won't create a bunch of OLM repo PRs.

[NissesSenap]

It's probably a good idea to look at https://github.com/grafana-operator/grafana-operator/issues/1313 first.

[NissesSenap]

Look at https://github.com/grafana/tempo-operator/blob/main/.github/workflows/reusable-operator-hub-release.yaml for inspiration