[feature]: create Negotiator RFQ service

[ffranr]

Parent issue: #683

From the parent issue:

This is the module that handles the actual negotiation. Given an offer (expressed in the tick unit, see the bLIP) it'll consult the PriceOracle for that given pair. For the PriceOracle we can either assume some set REST API to hit to obtain the price in a standard manner, or create a streaming RPC version of the PriceOracle. The operators of edge nodes would then use that RPC to feed in custom prices into their node. These RFQ messages are also forward-able, so operators may farm them off to various other sources to be able to take advantage of larger pools of liquidity.