Add Accept tests with IPLD media types

[lidel]

We now have block and CAR media types registered at IANA, would be good to include them in test suite:

• ?format=raw should also be tested with Accept header set to application/vnd.ipld.raw
• ?format=car should also be tested with Accept header set to application/vnd.ipld.car
• ?format=dag-json should also be tested with Accept header set to application/vnd.ipld.dag-json (Gateway support for dag-json and dag-cbor responses ipfs/kubo#8823)
• ?format=dag-cbor should also be tested with Accept header set to application/vnd.ipld.dag-cbor (Gateway support for dag-json and dag-cbor responses ipfs/kubo#8823)