allow adding IPv6 announced listen-IP and additional options to bbb-webrtc-sfu/production.yml

[einhirn]

Is your feature request related to a problem? Please describe.
Currently the role uses a rather static template file that only adds IPv4 addresses to webrtc-sfu config, so webrtc never uses IPv6 even though it could. There's no method to easily add further options.

With previous versions of this role, we had parts of the webrtc-sfu config file in our variables (excerpt):

mediasoup:
  webrtc:
    listenIps:
      - ip: "0.0.0.0"
        announcedIp: "{{ ansible_default_ipv4.address }}"
      - ip: "::"
        announcedIp: "{{ ansible_default_ipv6.address }}"
conference-media-specs:
  OPUS:
    maxaveragebitrate: '96000'

Describe the solution you'd like
For IPv6-listenIPs one might get away with a conditional block in the template? Same with additional options. There can of course be a "here be dragons" type warning attached to the latter...

Describe alternatives you've considered
Editing the file later in an add-on-role doesn't seem efficient, simply replacing it is also just a workaround...

[defnull]

The /etc/bigbluebutton/bbb-webrtc-sfu/production.yml file can be filly customized once #386 is merged. And I think ip6 should be added automatically, if configured. There is little to no reason not to offer ip6 for this case.