Support group sharing in Custos Sharing Manager

- Handle resolving Custos group
- add group membership to data product sharing view. We want a row in the view for every member of a group when an entity is shared with a group.

Start by locating the Custos Sharing Manager and the data product sharing view, then trace how shared entities and groups are currently resolved. The work is done when a group can be resolved and the sharing view shows one row for every group member; no tests or file paths are named in the issue.

Written by the indexing model from the issue text.