pulp_auth_proxy: Use stackhpc_release_pulp_url for Ark URL

This allows us to set stackhpc_repo_mirror_auth_proxy_enabled to true
while deploying the proxy without resulting in a recursive proxy.

Author: markgoddard

etc/kayobe/ansible/pulp-auth-proxy.yml

@@ -8,7 +8,7 @@
     - import_role:
         name: pulp_auth_proxy
       vars:
-        pulp_auth_proxy_url: "{{ stackhpc_repo_mirror_url }}"
+        pulp_auth_proxy_url: "{{ stackhpc_release_pulp_url }}"
         pulp_auth_proxy_username: "{{ stackhpc_repo_mirror_username }}"
         pulp_auth_proxy_password: "{{ stackhpc_repo_mirror_password }}"
         pulp_auth_proxy_conf_path: "{{ base_path }}/containers/pulp_proxy"