graph: Add support for filter users by displayName

[rhafer]

The /users endpoint should support the startswith and contains filters on the displayName attribute:

/user/$filter=startswith(displayName,'<filter>')
/user/$filter=contains(displayName,'<filter>')

In the LDAP identity backend these filters should translate into the corresponding LDAP filters. The libregraph spec needs to be updated accordingly.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 10 days if no further activity occurs. Thank you for your contributions.

[micbar]

@kulmann @tbsbdr

this is the prerequisite for filtered user lists in the admin UI.

I think we should limit the full listing to 200 and leave the page empty and prompt users for a filter. Can be seen in action in the keycloak user list in the admin menu.