Issue #3586257: Fix CacheableResponseSubscriber ignoring custom Cache-Control

Victor Weltersrequested to merge
issue/adv_varnish-3586257:3586257-cacheable-response-subscriber-respects-custom-cache-control into 4.x

Issue #3586257: Fix CacheableResponseSubscriber ignoring custom Cache-Control headers from controllers

Closes #3586257

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