Finding "authorized users" for a bucket should be optimized to run fewer permission filterning REST API requests

In order to populate the "authorized users" link in the bucket editing dialog the UI runs way too many requests to get users with permission filters.

We run this may REST API requests:

Each REST API request is actually fairly heavy as it needs to iterate over all users and tombstones in the users.dets file applying the permission filter.

It would be a lot better if we could pass an list of permissions with disjunction (i.e. "or") semantics.