feat: allow whitelisting of pubkeys for new events

This adds a configuration option, `authorization.pubkey_whitelist`
which is an array of pubkeys that are allowed to publish events on
this relay.

config.toml

@@ -65,3 +65,11 @@ reject_future_seconds = 1800
 # Event persistence buffer size, in number of events.  This provides
 # backpressure to senders if writes are slow.  Defaults to 16.
 #event_persist_buffer = 16
+
+[authorization]
+# Pubkey addresses in this array are whitelisted for event publishing.
+# Only valid events by these authors will be accepted.
+#pubkey_whitelist = [
+#  "35d26e4690cbe1a898af61cc3515661eb5fa763b57bd0b42e45099c8b32fd50f",
+#  "887645fef0ce0c3c1218d2f5d8e6132a19304cdc57cd20281d082f38cfea0072",
+#]