feat: limit event publishing to NIP-05 verified users

This adds a new configurable feature to restrict event publishing to
only users with NIP-05 verified metadata.  Domains can be whitelisted
or blacklisted.  Verification expiration and schedules are
configurable.

This upgrades the database to add a table for tracking verification
records.

src/lib.rs

@@ -5,6 +5,7 @@ pub mod db;
 pub mod error;
 pub mod event;
 pub mod info;
+pub mod nip05;
 pub mod protostream;
 pub mod subscription;
 pub mod tags;