Output-caching should support ETags #40226
Description
When configured, an eTag header will be generated. If the "If-None-Match" header is defined, a 304 response is returned.
When not configured, eTag values are not generated, and the "If-None-Match" header is ignored.
eTag might be generated on further requests only, to optimize for the first response (pass-through response writing without bufferization).