Add syslog integration

[laurivosandi]

On the VPN gateway interesting traffic could be logged to syslog and then forwarded to Certidude:

• Rejected traffic logged with rate limiting
• Start/stop of TCP/UDP sessions

Certidude could have another syslog server facilities, possibly use already deployed certificates to authenticate TLS tunnel for syslog and parse the messages coming in.

Parsed messages could be stored in SQL database with all relevant metadata decoded - who was the user/computer initiating the connections etc