Update to libp2p-0.23. (#6870)

* Update to libp2p-0.23.

Thereby incorporate bandwidth measurement along the
lines previously done by libp2p itself.

* Tweak dependencies for wasm32 compilation.

For wasm32 we need to enable unstable features to
make `task::Builder::local` available.

* Simplify dependencies.

* Simplify.

Leave the calculation of bytes sent/received per second
to the outer layers of the code, subject to their own
individual update intervals.

* Cleanup

* Re-add lost dev dependency.

* Avoid division by zero.

* Remove redundant metric.

* Enable sending of noise legacy handshakes.

* Add comment about monotonic gauge.

* CI