Add OVN migration OSP 16.2 option

In order to support OVN migration to OSP 16.2 we need to include
this option into OVN migraiton plugin spec file.

Change-Id: Ib52052d9a178a9246a83963cfa8e2c297ee0d94f
Closes-bug: #1912948

plugin.spec

@@ -46,6 +46,7 @@ subparsers:
                         - "15"
                         - "16"
                         - "16.1"
+                        - "16.2"
                         - kilo
                         - liberty
                         - mitaka