Deprecate linux bridge plugin

The os-vif linux bridge plugin is deprecated for removal
linux bridge support has been removed from neutron,
kyryr has been retired and nova network was removed 6 years ago.
as such there are no know user of this plugin remaining.

To facilate deprecation the linux_bridge plugin is retained for
the 2025.1 release cycle and a new warning is added on the first time
its used.

Change-Id: I69d1f618cbbbc4995fb3ea839fbaa9c850af1c77

releasenotes/notes/deprecate-linuxbridge-support-d278d4bbdff8e8bc.yaml

@@ -0,0 +1,7 @@
+---
+deprecations:
+  - |
+    The LinuxBridge mechanism driver has been removed in neutron. os-vif has a
+    policy of only shipping plugins for in-tree neutron ml2 drivers. As a result
+    the linux_bridge os-vif plugin is now deprecated and will be removed in
+    a future openstack release.

vif_plug_linux_bridge/linux_bridge.py

@@ -17,6 +17,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import debtcollector.removals
 from os_vif import objects
 from os_vif import plugin
 from oslo_config import cfg
@@ -94,6 +95,10 @@ class LinuxBridgePlugin(plugin.PluginBase):
                     supported_port_profiles=[]),
             ])
 
+    @debtcollector.removals.remove(
+        message="LinuxBridgePlugin is deprecated and will be removed in "
+                "a future release",
+        category=DeprecationWarning)
     def plug(self, vif, instance_info):
         """Ensure that the bridge exists, and add VIF to it."""
         network = vif.network
@@ -111,6 +116,10 @@ class LinuxBridgePlugin(plugin.PluginBase):
                 linux_net.ensure_bridge(bridge_name, iface,
                                         filtering=install_filters, mtu=mtu)
 
+    @debtcollector.removals.remove(
+        message="LinuxBridgePlugin is deprecated and will be removed in "
+                "a future release",
+        category=DeprecationWarning)
     def unplug(self, vif, instance_info):
         # Nothing required to unplug a port for a VIF using standard
         # Linux bridge device...