Introduce filter-based batch delete #416

There is a use case for batch-deleting several resources. One example is to go have a parent go delete all of the children of a parent resource - if the parent resource wanted to delete all of it's children in a given collection, it might use a REST API rather than perform whatever delete in the database directly.

The AIPs have batch delete today:

• https://google.aip.dev/235

That only has a way to go delete multiple specific IDs, but we could mix the filter AEP along with it:

• https://aep.dev/160/

This would require adding HTTP-based batch delete first. #45

CC @thegagne