* Adds x-directus-cache response header with HIT value
* Added ENV var for cache header and MISS, UNCACHEABLE
* Rename CACHE_HEADER_KEY -> CACHE_STATUS_HEADER
Tad opinionated, but I feel like it describes the functionality slightly better
* Return miss consistently
Uncacheable doesn't quite describe what's happening. The user actively requests the cache to be skipped, which should result in an expected miss. The value isn't un-cacheable, the cache is skipped on purpose
Co-authored-by: rijkvanzanten <rijkvanzanten@me.com>