Prior to this commit, Cache-Control HTTP headers could be set using
a WebContentInterceptor and configured cache mappings.
This commit adds support for cache-related HTTP headers at the controller
method level, by returning a ResponseEntity instance:
ResponseEntity.status(HttpStatus.OK)
.cacheControl(CacheControl.maxAge(1, TimeUnit.HOURS).cachePublic())
.eTag("deadb33f8badf00d")
.body(entity);
Also, this change now automatically checks the "ETag" and
"Last-Modified" headers in ResponseEntity, in order to respond HTTP
"304 - Not Modified" if necessary.
Issue: SPR-8550