bitswap/httpnet: request with CDN-Loop (RFC 8586)

We need to find a solution to situation where defunct gateways start returning redirects back to `ipfs.io` and `dweb.link`, effectively acting as amplification vector.

There is some prior art solution in form of `CDN-Loop` header which helps in avoiding unintended HTTP loops like that:

>
> This document defines the CDN-Loop request header field for HTTP.
> CDN-Loop addresses an operational need that occurs when an HTTP
> request is intentionally forwarded between Content Delivery Networks
> (CDNs), but is then accidentally or maliciously re-routed back into
> the original CDN causing a non-terminating loop. The new header
> field can be used to identify the error and terminate the loop.

Ref.
- https://datatracker.ietf.org/doc/html/rfc8586
- https://blog.cloudflare.com/preventing-request-loops-using-cdn-loop/
- https://github.com/ipfs/specs/issues/426

I think in case of Rainbow, we could leverage SEED and have all nodes set `CDN-Loop` to the same deterministic hash value, and refuse to process requests with matching one. This way HTTP traffic looped/proxied back to our infra is ignored.

cc @hsanjuan for feedback, maybe there a better way?