minor #15521 [FrameworkBundle] Update the default config of Doctrine cache (javiereguiluz)

This PR was merged into the 5.4 branch.

Discussion
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[FrameworkBundle] Update the default config of Doctrine cache

This complements #15520 and fixes the second part of #15505.

Commits
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bdf6ac6 [FrameworkBundle] Update the default config of Doctrine cache

Author: OskarStark

reference/configuration/framework.rst

@@ -2790,10 +2790,12 @@ annotations
 cache
 .....
 
-**type**: ``string`` **default**: ``'file'``
+**type**: ``string`` **default**: ``'php_array'``
 
 This option can be one of the following values:
 
+php_array
+    Use a PHP array to cache annotations in memory
 file
     Use the filesystem to cache annotations
 none