Boxo gateway should support IPIP-402 parameters

[hannahhoward]

What

Feature request. Boxo's gateway module should be updated to support the parameters and behavior described in ipfs/specs#402.

Specifically, for CAR requests, the gateway should:

• return intermediate blocks for the path when the request is for a cid+path
• support the car-scope parameter (including block, file, all)
• support the bytes parameter (lower priority -- not needed for the use case below)

Why

1. Lassie would like to retrieve from Boost over HTTP. Boost supplies an HTTP gateway by incorporating Boxo's gateway module. For Lassie to retrieve from Boost trustlessly, and serve all of the neccesary requests, the gateway must support the changes in IPIP-402, or at least everything except the bytes parameter. While we can certainly redirect to a shim for CAR requests, it seems like that would be very temporary solution and it would be better to just do it in Boxo.
2. CAR-based improvements to bifrost-gateway will be helped having a stable implementation to make calls against so can iterate against. Testing directly against not-yet-verified-if-spec-compliant Saturn adds in variables.
3. Implementations of IPIP-402 (e.g., Boxo, Kubo, bifrost-gateway, Lassie, Boost) want/need conformance tests. Given EngRes IP Stewards are driving the conformance tests, it's good to have a place they can quickly iterate on for validating the conformance tests.
4. Merging IPIP-402: Partial CAR Support on Trustless Gateways specs#402 requires having an accompanying client/server implementation to validate the work. Boxo is a natural place to do this work.

[BigLep]

I added more justification in the issue description for why this work should be done.