Deprecate support for networking-bigswitch

The networking-bigswitch plugin is unmaintained. The repo[1] has not
been updated for 2 years and no release has been created since Train.
Because we don't expect any user is using that unmainitained plugin
with recent versions of OpenStack, let's deprecate support for
the plugin so that we can remove it completely in the next cycle.

Closes-Bug: #1962579
Change-Id: Id4b07727af42b6a1d1145b71fc79f4bac7617eb3

manifests/agents/bigswitch.pp

@@ -1,5 +1,5 @@
 # == Class: neutron::agents::bigswitch
-#
+# DEPRECATED !!
 # Installs and configures the Big Switch agent and lldp
 #
 # === Parameters
@@ -26,6 +26,8 @@ class neutron::agents::bigswitch (
   include neutron::deps
   include neutron::params
 
+  warning('Support for networking-bigswitch has been deprecated.')
+
   if($::osfamily != 'Redhat') {
     fail("Unsupported osfamily ${::osfamily}")
   }

manifests/plugins/ml2/bigswitch.pp

@@ -1,4 +1,4 @@
-#
+# DEPRECATED !!
 # Install the Big Switch ML2 plugin.
 #
 # === Parameters
@@ -13,6 +13,8 @@ class neutron::plugins::ml2::bigswitch (
   $package_ensure = 'present',
 ) {
 
+  warning('Support for networking-bigswitch has been deprecated.')
+
   include neutron::deps
   include neutron::params
   require neutron::plugins::ml2

manifests/plugins/ml2/bigswitch/restproxy.pp

@@ -1,4 +1,4 @@
-#
+# DEPRECATED !!
 # Set config file parameters for connecting Neutron server to Big
 # Switch controllers.
 #

releasenotes/notes/deprecate-networking-bigswitch-8b617be7cf6ad2c7.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    Support for networking-bigswitch has been deprecated because the plugin is
+    unmaintained.