doc: update config with new allowed request destinations option

doc/config/yaml.yml

@@ -29,6 +29,8 @@ postal:
   smtp_relays: []
   # An array of IP addresses to trust for proxying requests to Postal (in addition to localhost addresses)
   trusted_proxies: []
+  # Hostnames or IP/CIDR ranges that outbound webhook and HTTP endpoint requests are permitted to reach even when they resolve to a private, loopback, link-local or otherwise reserved address. All other such destinations are blocked to prevent SSRF.
+  allowed_request_destinations: []
   # The number of days after which to consider a lock as stale. Messages with stale locks will be removed and not retried.
   queued_message_lock_stale_days: 1
   # When enabled queued messages will be de-queued in batches based on their destination