legacylibrarian: group multiple commits for the same library/piper origin ID

[parthea]

See PR googleapis/google-cloud-python#14671 where we have multiple entries for the same package and piper origin ID. The commit message is different, but everything else is the same. As an optimization, we could combine entries which have the same package and piper origin ID.

Current

BEGIN_NESTED_COMMIT
feat: [google-cloud-alloydb] update Database.charset to be immutable

PiperOrigin-RevId: 811874519

Source-link: [googleapis/googleapis@8cd7806](https://github.com/googleapis/googleapis/commit/8cd7806)
END_NESTED_COMMIT

BEGIN_NESTED_COMMIT
fix: [google-cloud-alloydb] An existing enum PoolMode is removed from the ConnectionPoolConfig

PiperOrigin-RevId: 811874519

Source-link: [googleapis/googleapis@8cd7806](https://github.com/googleapis/googleapis/commit/8cd7806)
END_NESTED_COMMIT

Proposed

BEGIN_NESTED_COMMIT
feat: [google-cloud-alloydb] update Database.charset to be immutable
fix: [google-cloud-alloydb] An existing enum PoolMode is removed from the ConnectionPoolConfig

PiperOrigin-RevId: 811874519

Source-link: [googleapis/googleapis@8cd7806](https://github.com/googleapis/googleapis/commit/8cd7806)
END_NESTED_COMMIT

[parthea]

Also see googleapis/google-cloud-python#14688

[JoeWang1127]

We decided to separate the commit into multiple nested commits in #2120.

Do we want to revert the change?

[julieqiu]

Closing since we do not plan to make this update to legacylibrarian.