New plugin for a TURN server (net/turnserver)

[fraenki]

Important notices
Before you add a new report, we ask you kindly to acknowledge the following:

• I have read the contributing guide lines at https://github.com/opnsense/plugins/blob/master/CONTRIBUTING.md
• I have searched the existing issues, open and closed, and I'm convinced that mine is new.
• When the request is meant for an existing plugin, I've added its name to the title.

Is your feature request related to a problem? Please describe.
A TURN server is required for several self-hosted video conferencing solutions (Nextcloud Talk, Jitsi Meet, BigBlueButton, Matrix, etc.). This service is pretty light-weight, but usually requires an excessive number of open ports. Besides that, running a TURN server behind NAT is not recommended.

Describe the solution you'd like
I plan to build a small plugin for net/turnserver. It consists of the net/turnserver port and a small GUI to adjust some options.

Describe alternatives you've considered
Running the TURN server elsewhere and using NAT, but this is not recommended.

Additional context
I've found a few requests on the forum regarding TURN servers behind a OPNsense firewall (NAT) and one request to run a TURN server directly on OPNsense. So I'm not the only one interested in this. :)

[fraenki]

$ ls -lh turnserver-4.6.2_1.pkg
-rw-r--r--  1 root wheel  545K Jan 15 22:45 turnserver-4.6.2_1.pkg

$ grep 'build time' turnserver-4.6.2_1.log
build time: 00:00:22

@fichtner The port is tiny and builds very fast, so the additional load on build servers and mirrors would be very low. Are there any objections from the core team regarding the addition of net/turnserver? Otherwise I would continue and create PRs for the new port/plugin (without database support, of course, to keep the number of dependencies low).