feat(NIP-42): pubkey authentication

Configurable in `config.toml`.  Limited functionality, but this does
send metadata to gRPC for event authorization.

fixes: https://todo.sr.ht/~gheartsfield/nostr-rs-relay/66

src/db.rs

@@ -30,6 +30,7 @@ pub struct SubmittedEvent {
     pub source_ip: String,
     pub origin: Option<String>,
     pub user_agent: Option<String>,
+    pub auth_pubkey: Option<Vec<u8>>,
 }
 
 /// Database file
@@ -240,7 +241,7 @@ pub async fn db_writer(
         if let Some(ref mut c) = grpc_client {
             trace!("checking if grpc permits");
             let grpc_start = Instant::now();
-            let decision_res = c.admit_event(&event, &subm_event.source_ip, subm_event.origin, subm_event.user_agent, nip05_address).await;
+            let decision_res = c.admit_event(&event, &subm_event.source_ip, subm_event.origin, subm_event.user_agent, nip05_address, subm_event.auth_pubkey).await;
             match decision_res {
                 Ok(decision) => {
                     if !decision.permitted() {