Add "explicit_domain_id" to api-ref

In [1] a new parameter to domain API was added. This patch
updates the api-ref about the same.

[1] https://review.opendev.org/#/c/605235/

Change-Id: If288c3406e2fa840f698fec83d9643cfc0584f53
Closes-Bug: #1884062

api-ref/source/v3/domains.inc

@@ -99,6 +99,7 @@ Parameters
 .. rest_parameters:: parameters.yaml
 
    - domain: domain
+   - explicit_domain_id: request_explicit_domain_id_body_not_required
    - enabled: domain_enabled_request_body
    - description: domain_description_request_body
    - name: domain_name_request_body

api-ref/source/v3/parameters.yaml

@@ -1721,6 +1721,15 @@ request_domain_options_body_not_required:
   in: body
   required: false
   type: object
+request_explicit_domain_id_body_not_required:
+  description: |
+    The ID of the domain. A domain created this way will not use an
+    auto-generated ID, but will use the ID passed in instead. Identifiers passed
+    in this way must conform to the existing ID generation scheme: UUID4 without
+    dashes.
+  in: body
+  required: false
+  type: string
 request_limit_domain_id_not_required:
   description: |
     The name of the domain.