Remove the bespoke instantiation of libp2p host and datatransfer manager
for index provider and reuse the existing instances used by markets.
The rationale for reuse is the following:
1. Separation of host introduces a discovery problem, where without
gossipsub the index provider endpoint will not be discoverable.
Using the same host as markets would mean the chain can be used to
discover addresses, putting less empassis on criticality of
gossipsub considering its set-up cost and lack of message delivery
guarantees.
2. Only a single instance of graphsync/datatransfer can be instantiated
per libp2p host; therefore, if the host is shared, so should
datatransfer manager.
3. it is not clear if the assumptions under which separation was
decided still hold.
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