Add echobot, chatmail-metadata, and iroh-relay to diagram

Author: cliffmccarthy

ARCHITECTURE.md

@@ -18,12 +18,15 @@ graph LR;
     postfix --> certs;
     postfix --> vmail;
     postfix --> filtermail;
+    postfix --> echobot;
     postfix --> doveauth;
     dovecot --> certs;
     dovecot --> doveauth;
     dovecot --> vmail;
+    dovecot --> chatmail-metadata;
     doveauth --> vmail;
     expunge --> vmail;
+    chatmail-metadata --> iroh-relay;
 ```
 
 (Arrows in this diagram do not have a specific formal meaning; they