share/discovery: consider withdrawing connecting responsibility from Discovery

Discovery currently discovers and connects to peers. The goal is to make it work for Bitswap to catch up on those connections and sample from them. However, Discovery should not make connections and only provide peers, as connecting is the protocol's responsibility. This should also improve shrex protocols giving them more control.

The only way to do it is by enabling discovery in bitswap using a custom implementation that returns discovered peers for any requested CID