Warnings on portforward sync

[jasperslits]

Steps to reproduce

1. Go to Unifi Network
2. Go to Firewall & security
3. Enable or disable an existing port forwarding rule
4. Check home assistant system log

This emits a warning upon saving:
2023-06-23 13:26:51.694 WARNING (MainThread) [aiounifi.models.message] Unsupported message key portforward:sync
2023-06-23 13:26:51.694 WARNING (MainThread) [aiounifi.models.message] Unsupported message {'meta': {'rc': 'ok', 'message': 'portforward:sync'}, 'data': {'pfwd_interface': 'wan', 'fwd': '192.168.178.XXX', 'destination_ip': 'any', 'src': 'any', 'log': False, 'proto': 'tcp', 'name': 'Certbot', 'dst_port': '80', 'site_id': 'XXX', '_id': 'XXX', 'fwd_port': '80', 'enabled': True}}

Versions:
Unifi OS: 3.1.9 on UDM PRO
Network: Unifi Network Application 7.4.156
Home Assistant: 2023.6.2

It makes sense as models/message.py does not include portforward:sync in the MessageKey class, so are you OK if I submit a PR to include portforward?

Now the other part is perhaps to assess what value it brings to Home Assistant user if you update / create a port forwarding. E.g. is a user going to use it in an automation? So perhaps the warning should be a changed to debug or just info? Seeing it's harmless.

[jasperslits]

I created #391 for this