add context to mqtt client connected message

runtime/binding-mqtt/src/main/java/io/aklivity/zilla/runtime/binding/mqtt/internal/MqttEventFormatter.java

@@ -48,7 +48,7 @@ public String format(
         case CLIENT_CONNECTED:
         {
             MqttClientConnectedExFW ex = extension.clientConnected();
-            result = String.format("%s %s", identity(ex.identity()), asString(ex.clientId()));
+            result = String.format("Session authorization (%s) was successful for client id (%s).", identity(ex.identity()), asString(ex.clientId()));
             break;
         }
         }

specs/binding-mqtt.spec/src/main/scripts/io/aklivity/zilla/specs/binding/mqtt/config/server.log.event.yaml

@@ -25,7 +25,7 @@ telemetry:
                     - qname: test.net0
                       id: binding.mqtt.client.connected
                       name: BINDING_MQTT_CLIENT_CONNECTED
-                      message: "- client"
+                      message: Session authorization (-) was successful for client id (client).
 bindings:
     net0:
         type: mqtt