Add option to endpoints that retrieve sessions to skip hostname lookup

[guusdk]

Endpoints that return (client) sessions return entities that have a hostname field. To populate this field, a DNS lookup is sometimes required. This can severely slow down the response to requests on systems that have many sessions.

An optional request argument should be added that prevents this lookup.

[guusdk]

As requested in https://discourse.igniterealtime.org/t/rest-api-sessions-endpoint-slow/