Follow-up of #9811 (comment).

When a new library for a service is created, it calls generate_gapic_bom.sh:

    subprocess.check_call(
        [
            "bash", "generation/generate_gapic_bom.sh",
        ],
        cwd=monorepo_root,
    )

This script adds the newly generated library as part of gapic-libraries-bom/pom.xml.