playbook_provision_gateway: add base file functionality

a file in "base" will be distributed to all gateways but can still be
overriden by a device specific file in $inventory_hostname.

This should enable some config sharing

playbook_provision_gateway.yml

@@ -22,6 +22,7 @@
         group: root
         mode: 0600
       with_fileglob:
+        - "templates/gateways/base/etc/config/*"
         - "templates/gateways/{{ inventory_hostname }}/etc/config/*"
       notify:
         - "reload {{ item | basename }}"
@@ -34,6 +35,7 @@
         group: root
         mode: 0600
       with_fileglob:
+        - "templates/gateways/base/etc/frr/*"
         - "templates/gateways/{{ inventory_hostname }}/etc/frr/*"
       notify:
         - restart frr