H264: pull out and fold Janus-logic into `ansible-role-ustreamer`

[jotaen4tinypilot]

As discussed, we wanted to go with “solution 3”, which is to fold over the Janus-related logic from ansible-role-tinypilot to ansible-role-ustreamer. That way, ansible-role-ustreamer fully controls the Janus service, and is able to restart it after configuration changes. This is needed for applying an H264 bitrate change.

Notes:

• If we merge the corresponding PR in ansible-role-ustreamer first, then we can remove the dependency pin in requirements.yml here.
• Currently, we don’t have an existing way to start the Janus server at a specific interface (e.g. 127.0.0.1). Therefore, I hard-coded the value in the nginx configuration for now.