Add documentation for new --all option for cache:pool:clear

Author: bobvandevijver

cache.rst

@@ -725,6 +725,14 @@ Clear all custom pools:
 
     $ php bin/console cache:pool:clear cache.app_clearer
 
+Clear all cache pools:
+
+    $ php bin/console cache:pool:clear --all
+
+.. versionadded:: 6.3
+
+    The `--all` option was introduced in Symfony 6.3.
+
 Clear all caches everywhere:
 
 .. code-block:: terminal