minor symfony#17052 [HttpFoundation] Add cache option (sfmok)

This PR was merged into the 4.4 branch.

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[HttpFoundation] Add cache option

Add `immutable` cache option

Commits
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cd2188a [HttpFoundation] Add cache option

Author: javiereguiluz

http_cache.rst

@@ -356,6 +356,7 @@ Additionally, most cache-related HTTP headers can be set via the single
         's_maxage'      => 10,
         'public'        => true,
         // 'private'    => true,
+        'immutable'      => true,
     ]);
 
 Cache Invalidation