docs: Document MQTT support for printer objects

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

docs/configuration.md

@@ -559,6 +559,23 @@ instance_name:
 #   Responses will be published to the following topic:
 #     my_printer/moonraker/api/response
 #   The default is the machine's hostname.
+status_objects:
+#   A newline separated list of Klipper objects whose state will be
+#   published in the payload of the following topic:
+#      {instance_name}/klipper/status
+#   For example, to track the "webhooks" and "toolhead" objects this
+#   option would be set as follows:
+#     status_objects:
+#       webhooks
+#       toolhead
+#   See the "Printer Objects" section of the documentation for an
+#   overview of the most common objects available.  Note that Klipper
+#   will only push an update to an object/field if the field has changed.
+#   An object with no fields that have changed will not be part of the
+#   payload.  Object state is checked and published roughly every
+#   250 ms.
+#   If not configured then no objects will be tracked and published to
+#   the status topic.
 default_qos: 0
 #   The default QOS level used when publishing or subscribing to topics.
 #   Must be an integer value from 0 to 2.  The default is 0.

docs/web_api.md

@@ -321,8 +321,9 @@ POST /printer/objects/subscribe?connection_id=123456789&gcode_move&extruder`
     request that includes only the `connection_id` argument will cancel the
     subscription on the specified websocket.
 
-    This request is not available over MQTT, as it is not possible to
+    This request is not available over MQTT as it can not be set per client.
-    associate a connected websocket with an MQTT client.
+    Instead MQTT can publish printer status by setting the `status_objects`
+    option in the `[mqtt]` section.
 
 JSON-RPC request:
 ```json