refactor: WireGuard tunnels are read in their own module (#32)

get_vpn_tunnels() grew past the quality baseline with the key fix. The
WireGuard part is pure parsing of /api/wireguard/service/show, like the
listen ports in listening.py, so it moves to wireguard.py and the driver
calls it. opnsense.py shrinks from 3125 to 3082 lines.

tests/quality_baseline.json

@@ -24,7 +24,7 @@
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_lldp_neighbors_detail": 12,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_networks": 25,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_route_to": 23,
-  "napalm_opnsense/opnsense.py::OPNsenseDriver.get_vpn_tunnels": 60,
+  "napalm_opnsense/opnsense.py::OPNsenseDriver.get_vpn_tunnels": 47,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.load_merge_candidate": 13,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.sync_dns_zone": 20,
   "napalm_opnsense/port_forwards.py::_forwards_of": 12,
@@ -43,7 +43,7 @@
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_interfaces_ip": 68,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_networks": 85,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_route_to": 85,
-  "napalm_opnsense/opnsense.py::OPNsenseDriver.get_vpn_tunnels": 189,
+  "napalm_opnsense/opnsense.py::OPNsenseDriver.get_vpn_tunnels": 145,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.load_merge_candidate": 56,
   "napalm_opnsense/opnsense.py::OPNsenseDriver.sync_dns_zone": 112
  },
@@ -57,7 +57,7 @@
   "napalm_opnsense.resolver_mixin"
  ],
  "python_file_lines": {
-  "napalm_opnsense/opnsense.py": 3125
+  "napalm_opnsense/opnsense.py": 3082
  },
  "untyped_public": [
   "napalm_opnsense/opnsense.py::OPNsenseDriver.get_snmp_config"