Keystone v3-ext/OS-ENDPOINT-POLICY endpoints implementation.

Existing policy client is missing policy association API calls
for the endpoints, services and regions. These are supported API,
as mentioned on the wiki given below:

https://developer.openstack.org/api-ref/identity/v3-ext/index.html#associate-policy-and-endpoint

Closes-Bug: #1682641
Change-Id: I4af1e4862a17216d65446e8c29bd1b886f5d8c24
diff --git a/releasenotes/notes/add-additional-methods-to-policy-client-library-b8279c18335588c9.yaml b/releasenotes/notes/add-additional-methods-to-policy-client-library-b8279c18335588c9.yaml
new file mode 100644
index 0000000..cd5284d
--- /dev/null
+++ b/releasenotes/notes/add-additional-methods-to-policy-client-library-b8279c18335588c9.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Add ``v3-ext/OS-ENDPOINT-POLICY`` API calls to support creation, deletion and
+    retrieval of associations between service endpoints and policies. Such associations
+    enable an endpoint to request its policy.