Network mux demo for analysing Leios/Praos traffic

[coot]

We need a demo network-mux application that runs two mini-protocols to emulate Leios and Praos traffic. This demo can then be used to provide data for analysing traffic when using MUX with prioritisation capabilities and/or rate limiting. Later, this demo can also be helpful when we need to provide an initial MUX configuration with these capabilities for a real node; however, it should not substitute for an analysis of a real deployment late in the development cycle of a Leios-capable cardano-node.