Neutron: support BGP VPN service

Add ability to enable BGP VPN service and configure driver for it.
Corresponding model change: https://gerrit.mcp.mirantis.net/#/c/15779

Change-Id: I362d12efa49ef8c8b5b6d0352dc11863e0f63311
Related-Prod: PROD-17612
diff --git a/neutron/compute/cluster.yml b/neutron/compute/cluster.yml
index 13ee31c..e348a93 100644
--- a/neutron/compute/cluster.yml
+++ b/neutron/compute/cluster.yml
@@ -4,6 +4,8 @@
   _param:
     neutron_enable_qos: False
     neutron_enable_vlan_aware_vms: False
+    neutron_enable_bgp_vpn: False
+    neutron_bgp_vpn_driver: bagpipe
   linux:
     system:
       package:
@@ -15,6 +17,9 @@
       dvr: ${_param:neutron_compute_dvr}
       qos: ${_param:neutron_enable_qos}
       vlan_aware_vms: ${_param:neutron_enable_vlan_aware_vms}
+      bgp_vpn:
+        enabled: ${_param:neutron_enable_bgp_vpn}
+        driver: ${_param:neutron_bgp_vpn_driver}
       agent_mode: ${_param:neutron_compute_agent_mode}
       external_access: ${_param:neutron_compute_external_access}
       backend: