Deprecate support for staging driver

ironic-staging-driver[1] is unmaintained. The repository does not have
stable branches created since yoga.

It was asked if anyone is using this driver in the mailing list but
we haven't heard any response.

[1] https://opendev.org/x/ironic-staging-drivers#
[2] https://lists.openstack.org/archives/list/openstack-discuss@lists.openstack.org/message/S4UYAPCPVXWEC6RDJ4GLTFCFT5XTCVQG/

Change-Id: I41a8aebe24aa4155c2e5029b187a2ba43ebb313b

manifests/drivers/staging.pp

@@ -15,6 +15,8 @@ class ironic::drivers::staging (
   include ironic::deps
   include ironic::params
 
+  warning('Support for staging driver has been deprecated and will be removed in a future release.')
+
   if $::ironic::params::staging_drivers_package {
     package { 'ironic-staging-drivers':
       ensure => $package_ensure,

releasenotes/notes/deprecate-staging-b41fc5da465b559b.yaml

@@ -0,0 +1,4 @@
+---
+deprecations:
+  - |
+    Support for staging driver has been deprecated.