[snrc resolver] report expiry and availability correctly

[brenzi]

Problem with #1860 alone: It prepares the resolver to be used to query availability of names without revealing them, but the response can be misleading because we don't handle expiry and reserved status meaningfully.

• An expired name beyond its grace period would still resolve although it is actually available again.
• Reserved names would show as available although they aren't
• taken-but-resolverless name 404s identically to a free one

This PR fixes the problems above

• report expiry and reserved status (preparing for reporting a specific reason)
• introduce meaningful http error codes and handle them in Names.hs