Rename debug_cacheability_headers to something meaningful

Problem/Motivation

To use cachetags on a Drupal 8 site, you need to add http.response.debug_cacheability_headers: true to services.yml. Everything is in a name, and for me cachetags are not a debug setting, it is a feature, so it should be named in a way that describes what it is.

Proposed solution

My suggestion is to rename http.response.debug_cacheability_headers to http.response.enable_cacheability_headers, HttpResponseDebugCacheability to HttpResponseEnableCacheabilityHeaders.