Built in MatrixRTC/Element Call support

[ShadowRocket227]

I keep having trouble configuring my Tuwunel for supporting MatrixRTC/Element Call, the new technology for audio and video calls on Matrix. I currently had to fallback on the legacy calls, and this means that I also had to give up Element X and other modern clients because they don't support legacy calls anymore.

I know that you can configure livekit etc manually and make this work, but personally I was never able to figure it out, and besides of this I think that supporting officially MatrixRTC would really contribute to make Tuwunel the best Matrix homeserver around. I think that only Synapse fully supports it!