WebRTC relay mode configuration

[evdokimovs]

Part of #27

Synopsis

RTCPeerConnection can be configured to relay all media through TURN server. This behavior is managed by RTCIceTransportPolicy.

This PR adds opportunity to enable relay mode of RTCPeerConnection by Control API.

Solution

• 1. Add is_relay to the Control API
• 2. Add is_relay into Event::PeerCreated in the Client API
• 3. Based on Event::PeerCreated::is_relay select RTCIceTransportPolicy "all" (if is_relay is false) or RTCIceTransportPolicy "relay" (if is_relay is true)

Checklist

• Created PR:
  • In draft mode
  • Name contains WIP: prefix
  • Name contains issue reference
  • Has k:: labels applied
  • Has assignee
• Documentation is updated (if required)
• Tests are updated (if required)
• Changes conform code style
• CHANGELOG entry is added (if required)
• FCM (final commit message) is posted
  • and approved
• Review is completed and changes are approved
• Before merge:
  • Milestone is set
  • PR's name and description are correct and up-to-date
  • WIP: prefix is removed
  • All temporary labels are removed

[evdokimovs]

FCM

WebRTC relay mode configuration (#79)

- add 'force_relay' field into Client API's Event::PeerCreated
- add 'force_relay' field into Control API's WebRtcPublishEndpoint and WebRtcPlayEndpoint
- configure RTCIceTransportPolicy basing on 'force_relay' option
- add 'force_relay' mode selection into 'e2e-demo' Control API UI 
- add 'force_relay' option support into 'medea-control-api-mock'