We should automatically suggest PRs for libraries in v1 or stable and have had 30 days opened

[sofisl]

See issues like: https://github.com/googleapis/google-cloud-node/issues/3956 and https://github.com/googleapis/google-cloud-node/issues/3541

We still need to manually check for upgrades. Instead, we should create an action that automatically promotes the library iff:

• it's been open for at least 30 days
• has a v1 or greater version

[sofisl]

This issue is outdated because we don't use .repo-metadata.json anymore. But, we still have the need to auto-update libraries to stable here. for example