bitswap/httpnet: add WithDenylist option

[lidel]

We have ability to enable HTTP retrieval for specific hostnames (only do HTTP with hosts from allowlist) via httpnet.WithAllowlist

To prepare for the future where we enable this by default in places like Kubo, there should be a companion, opposite flag that allows us to pass explicit denylist (with known hosts that should NOT be used for HTTP retrieval) – httpnet.WithDenylist

The denylist should apply to both original URL and any HTTP redirects.

The main reason here is to avoid situation where defunct gateways start returning redirects to ipfs.io and dweb.link, effectively acting as amplification vector (note: there may be a better fix in #862).

cc @hsanjuan