Allow using cardano-cli to interact with Hydra Head

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Why

cardano-cli is a useful general purpose tool to build and submit transactions, and query the state of the ledger. It uses cardano-node's local mini-protocol stack which is exposed through a local socket to interact with the node. Other commonly used tools (eg. Ogmios, Daedalus,...) also rely on such an interface to provide additional services to users/builders.

While not all of the node-2-client mini-protocols would be relevant to a Hydra head, implementing the basics like transaction submission, querying UTxO, or even "mempool" monitoring, would certainly be useful and lower the barrier of entry to Hydra as people would be able to use tools they know.

What

Have hydra-node expose (part of) node-to-client mini protocols stack on a local socket that could be used by cardano-cli to submit transactions and query UTxO.

How

As hydra-node already uses Ouroboros network stack, we could reuse the n2c part of the mini-protocols and implement the various "servers", wherever appropriate.