minor #21590 [Cache] Clarify #[Cache] attribute precedence behavior (ayyoub-afwallah)

This PR was submitted for the 7.4 branch but it was merged into the 6.4 branch instead.

Discussion
----------

[Cache] Clarify `#[Cache]` attribute precedence behavior

Adds tip explaining that #[Cache] attribute doesn't override manually set headers.

Related to [#62488](symfony/symfony#62488)

Commits
-------

9c6197e Clarify `#[Cache]` attribute precedence behavior

Author: javiereguiluz

http_cache.rst

@@ -239,6 +239,10 @@ Thanks to this new code, your HTTP response will have the following header:
 
     Cache-Control: public, maxage=3600, must-revalidate
 
+.. tip::
+
+    When both are used, the cache headers defined in the controller take precedence over those configured with the `#[Cache]` attribute.
+
 This tells your HTTP reverse proxy to cache this response for 3600 seconds. If *anyone*
 requests this URL again before 3600 seconds, your application *won't* be hit at all.
 If you're using the Symfony reverse proxy, look at the ``X-Symfony-Cache`` header