[placement] api-ref: Add missing aggregates example

About "PUT /resource_providers/{uuid}/aggregates"
in the Placement API reference,
the example of the response body in microversion 1.1 - 1.18 is missing.
So add it.

Change-Id: Ic3dc665124ae7927cfa20cf70a08c39b856b8961
Closes-Bug: #1786759

placement-api-ref/source/aggregates.inc

@@ -135,14 +135,20 @@ Request example (microversion 1.19 - )
 .. literalinclude:: ./samples/aggregates/update-aggregates-request-1.19.json
    :language: javascript
 
-Response (microversion 1.19 - )
-----------------------------------
+Response (microversion 1.1 - )
+------------------------------
 
 .. rest_parameters:: parameters.yaml
 
   - aggregates: aggregates
   - resource_provider_generation: resource_provider_generation_v1_19
 
+Response Example (microversion 1.1 - 1.18)
+------------------------------------------
+
+.. literalinclude:: ./samples/aggregates/update-aggregates.json
+   :language: javascript
+
 Response Example (microversion 1.19 - )
 ------------------------------------------