Add mplex protocol to libp2p stack

[flcl42]

Protocol implementation request: mplex

• Stack: standard libp2p
• Type: multiplexer, transport layer
• Specification: https://github.com/libp2p/specs/blob/master/mplex/README.md

Additional context Mplex protocol should be considered as an alternative to yamux during protocol selection.

How to add new protocol guide

[flcl42]

Not plans to implement