[db-wg] Support for recursive expansion of as-set to a list of ASNs

Dear DB-WG, Now that the new database backend is in place, this should allow for awesome features such as server sided recursion of AS-SETs into a list of ASNs. Implementing IRRd's !i flag will prevent a lot of back and forth communication between whois server and client to provide the client with a full list of ASNs which are part of an AS-SET. Clients such as bgpq3 support this flag. I've filed an enhancement request on github: https://github.com/RIPE-NCC/whois/issues/72 But we could use this thread to assess community support and gather a sense of priority. Kind regards, Job