Add github action to rerun codegen that triggers on a grafana release

[sdboyer]

To keep grok in sync with grafana, we need a github action that:

• Is triggered upon a new release of Grafana (OSS releases should be enough, we can add cloud releases as those become available)
• Runs the main grok code generator to spit out the latest and greatest
• Commits the result, opens a PR with the changes

Almost certainly depends on grafana/grafana#58498

cc @malcolmholmes