Document query option (is_domain) for projects

The "is_domain" query parameter is missing from GET/UPDATE /v3/projects
documentation in the API site.

Change-Id: I059f7e2ac689ec799dbdcc30c071de26d1603c47
Closes-bug: #1609174

api-ref/source/v3/parameters.yaml

@@ -229,6 +229,15 @@ interface_2:
   in: query
   required: false
   type: string
+is_domain_query:
+  description: |
+    If this is specified as true, then only projects acting as a domain are
+    included. Otherwise, only projects that are not acting as a domain are
+    included.
+  in: query
+  required: false
+  type: boolen
+  min_version: 3.6
 name_10:
   description: |
     Filters the response by a domain name.

api-ref/source/v3/projects.inc

@@ -44,6 +44,7 @@ Request
 
    - domain_id: domain_id_query
    - enabled: project_enabled_query
+   - is_domain: is_domain_query
    - name: project_name_query
    - parent_id: parent_id_query
 
@@ -174,6 +175,7 @@ Request
 
    - project_id: project_id_path
    - project: project
+   - is_domain: is_domain_request_body
    - description: project_description_request_body
    - domain_id: project_domain_id_update_request_body
    - enabled: project_enabled_update_request_body