Fuseki to send `ETag` response headers

### Version

4.7.0

### Feature

Graphs without bnodes can be safely hashed and the hash can be used as a strong `ETag` value.
Graphs with bnodes can be hashed and the hash could be used as a weak `ETag` value?

### Are you interested in contributing a solution yourself?

Perhaps?

Start at Fuseki's HTTP response handling and inspect how graph content and hashing are currently represented; the issue names no specific files or tests. Define the strong versus weak ETag behavior for graphs with and without blank nodes, then add response coverage showing the intended headers.

Written by the indexing model from the issue text.