[placement] Add 'Location' parameters in API ref

The 'Location' parameters are missing in the follwoing APIs of
Placement API reference. So add them.

* POST /resource_providers
* POST /resource_classes
* PUT /resource_classes/{name} (microversion 1.7-)
* PUT /traits/{name}

Change-Id: Ieed5cb7d4697472ab46b2e80d6d2df68098c5631
Closes-Bug: #1733329

placement-api-ref/source/parameters.yaml

@@ -1,3 +1,12 @@
+# variables in header
+location:
+  description: |
+    The location URL of the resource created,
+    HTTP header "Location: <Location URL>" will be returned.
+  in: header
+  required: true
+  type: string
+
 # variables in path
 consumer_uuid: &consumer_uuid
   type: string

placement-api-ref/source/resource_class.inc

@@ -69,6 +69,10 @@ Request
 Response
 --------
 
+.. rest_parameters:: parameters.yaml
+
+  - Location: location
+
 No body content is returned on a successful PUT.
 
 Update resource class (microversions 1.2 - 1.6)

placement-api-ref/source/resource_classes.inc

@@ -68,4 +68,8 @@ Request example
 Response
 --------
 
+.. rest_parameters:: parameters.yaml
+
+  - Location: location
+
 No body content is returned on a successful POST.

placement-api-ref/source/resource_providers.inc

@@ -83,4 +83,8 @@ Request example
 Response
 --------
 
+.. rest_parameters:: parameters.yaml
+
+  - Location: location
+
 No body content is returned on a successful POST.

placement-api-ref/source/traits.inc

@@ -99,6 +99,10 @@ Request
 Response
 --------
 
+.. rest_parameters:: parameters.yaml
+
+  - Location: location
+
 No body content is returned on a successful PUT.
 
 Delete traits