Add support for ETag and If-None-Match to GET /node/ledger-chunk/{chunk_name}

[achamayou]

Use the example and library functions added in #6110 to implement ETags for the GET /node/ledger-chunk/{chunk_name} endpoint.

ETag values for this endpoint must be of the form "algorithm:digest" where algorithm is one of sha-256, sha-384 or sha-512, and digest is the hexadecimalrepresentation of the digest of the content, using that same algorithm.
When computing the default ETag response header, use sha-256, but when clients pass an If-None-Match request header, all three digest algorithms must be accepted and supported.

The ETag (and corresponding If-None-Match behaviour) must be over the content, potentially restricted by the Range header, not necessarily the full file.