GHA: Open PR to podman-machine-os on releases

When we do a release, we need to ensure that machine images are built before the release PR can merge.

This GitHub action is triggered on version bumps, waits for our COPR builds to finish, and then opens a PR on the podman-machine-os repo to build the required machine-os images there. Note that dev bumps, unless on main, will not open a PR

Signed-off-by: Ashley Cui <[email protected]>