Deprecate support for designate-agent

The agent framework and drivers have been deprecated in Designate
during Antelope cycle. See the dependent change for further details.

Depends-on: https://review.opendev.org/872716
Change-Id: Id0fc93fde98fafc4dc79a38982dd5ca844a4b049

manifests/agent.pp

@@ -1,5 +1,6 @@
 # == Class designate::agent
 #
+# DEPRECATED !!
 # Configure designate agent service
 #
 # == Parameters
@@ -49,6 +50,8 @@ class designate::agent (
 
   include designate::deps
 
+  warning('The agent framework has been deprecated.')
+
   designate_config {
     'service:agent/backend_driver' : value => $backend_driver;
     'service:agent/workers' :        value => $workers;

manifests/agent/bind9.pp

@@ -1,5 +1,6 @@
 # == Class designate::agent::bind9
 #
+# DEPRECATED !!
 # Configure bind9 as agent backend
 #
 # == Parameters
@@ -44,6 +45,8 @@ class designate::agent::bind9 (
 
   include designate::deps
 
+  warning('The agent framework has been deprecated.')
+
   designate_config {
     'backend:agent:bind9/rndc_host'         : value => $rndc_host;
     'backend:agent:bind9/rndc_port'         : value => $rndc_port;

manifests/backend/agent.pp

@@ -1,5 +1,6 @@
 # == Class designate::backend::agent
 #
+# DEPRECATED !!
 # Configure agent as backend
 #
 # == Parameters
@@ -35,6 +36,8 @@ class designate::backend::agent (
   include designate::deps
   include designate::params
 
+  warning('The agent framework has been deprecated.')
+
   if $manage_pool {
     file { '/etc/designate/pools.yaml':
       ensure  => present,

releasenotes/notes/deprecate-agent-framework-c8d8e5017ebb8851.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    Support for the ``designate-agent`` service and the ``agent`` backend has
+    been deprecated, because the framework has been deprecated in Designate.