This PR aims to add `Vary` header in Thumbor response to avoid problems with downstream caches.

Closes https://github.com/thumbor/thumbor/issues/1563
thanks @mpdude 
Should have vary header with auto heif and avif. This PR aims to add `Vary` header in Thumbor response to avoid problems with downstream caches.

Closes https://github.com/thumbor/thumbor/issues/1563
thanks @mpdude 
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