Lot's of redundant LDAP queries of listing all groups with members

## Describe the bug

A graph request to list all groups with member expanded, becomes very expensive quickly:

`https://localhost:9200/graph/v1.0/groups?$expand=members`

This is partially caused by the backend doing no caching at all, which e.g. means that it is resolving every user that is a member of multiple groups multiple times :cry: (we should at least avoid that to happen within a single graph request)

But the full truth is that this will always be an expensive query. I think we should enforce a limit of results we return from such a query and introduce support for filters for the graph/groups endpoint. (From a larger numbers of groups and users, listing all of them at once does not provide much value anyway)