Add Hydrogen GroupCalls shim for easily testing game networking

[robertlong]

In https://github.com/matrix-org/thirdroom/pull/607/commits/aee3677c81ac805128349744536925cfc7b23a4d I removed our Test Net adapter which used a websocket to forward networking packets between clients while working locally. This is nice because it allows you to test if a networking issue is related to WebRTC or Hydrogen and rapidly test without waiting to connect via Matrix. It'd be nice to add this feature back into Third Room at some point.