Add YAML format into docs for policy file

kolla-ansible support yaml format for policy file[1] too, but the
docs missing it, this ps to add it.

[1]: https://github.com/openstack/kolla-ansible/blob/master/ansible/group_vars/all.yml#L393
Closes-Bug: #1804455

Change-Id: I44eb1d64f9299ccaf99972c8b5354683a3501f6b

doc/source/admin/advanced-configuration.rst

@@ -217,7 +217,7 @@ and then put it to ``/etc/kolla/config/neutron/policy.json``.
 
 .. note::
 
-   Currently kolla-ansible only support JSON format for policy file.
+   Currently kolla-ansible only support JSON and YAML format for policy file.
 
 The operator can make these changes after services were already deployed by
 using following command: