There was no point requesting the key frame by sending a message to the
conference as the only thing that the conference did was calling a
single function from the peer, so it was completely wasting the CPU
time. Instead, we could directly call this function and write to the
peer connection. The function is thread-safe since all mutable state is
protected by a mutex and the peer connection has a mutex inside.

This solves the problem with managing the queue size on the receiver.

It's ok if the matrix SDK blocks until we're ready to accept new
messages.

Use unbounded channels for that. We can't quite use it for the
multi-conference set ups as a single conference will affect others, but
currently we don't have these problems.

Usage of `common` is an anti-pattern.

Package `common` is an antipattern.

The `common` package is an antipattern.

This is a temporary measure until we can workaround bugs in Pion that
lead to the deadlocks.

So it better reflects the semantics (that the function does not block).