Support IPIP-417 (Delegated Peer lookups)

[BigLep]

Done Criteria

IPIP-417 (Delegated Peer lookups) support, meaning could delegate peer lookups with another HTTP /routing/v1 implementation like Kubo

Why Important

This is needed for the Helia reliable retrieval golden path scenario: ipfs/helia#255

[achingbrain]

This is an implementation of the libp2p ContentRouting interface.

Peer lookups would be done by an implementation of the libp2p PeerRouting interface so this isn't the place to do that.

We might end up getting @helia/delegated-routing-v1-http-api to make implementations of both of these interfaces available after all since passing the same instance as contentRouters and peerRouters is a bit icky.