Add a filter parameter for bump_packages

[ekohl]

Applying this filter allows calling it from a specific plugin to only update a single package. For example, when a gem is released it can automatically trigger this workflow.

Right now the actual scripts don't implement this, so this is just a proposal. My idea is that we enhance our release-gem workflow to trigger a packaging bump. That way we don't update all existing PRs but still have nice end-to-end automation for nightly. Stable branches still need additional work.