upper-bound-check to work with google-cloud-java's split repository in more generic way

Regarding google-cloud-java's split repositories, as of now the upper-bound-check (https://github.com/googleapis/google-cloud-java/pull/6606/files) does not work for individual libraries, because the libraries-bom only references google-cloud-bom's version. It cannot update individual library's versions referenced by google-cloud-bom.

@chingor13 says:

> it seems like we might be able to generalize it to check for arbitrary artifacts with any bom
so like the pubsub repo could check itself in google-cloud-bom

Note that, contrary to upper-bound-check, Linkage Monitor should work for the individual repositories.