Clarify Symfony flex limitations (#14836)

Author: cleptric

docs/platforms/php/guides/symfony/configuration/symfony-options.mdx

@@ -89,8 +89,7 @@ sentry:
 ```
 
 The DSN option is the only required option: it sets the Sentry DSN, and so reports all events to the related project. If it's
-left empty, it disables Sentry reporting. Because Sentry enables the bundle in all environments, it's recommended to
-disable it in the `test` and `dev` environments.
+left empty, it disables Sentry reporting.
 
 All the possible configurations under the `options` key map directly to the correspondent options from the base SDK;
 you can read more about those in the [general configuration docs](../options/).

docs/platforms/php/guides/symfony/index.mdx

@@ -29,6 +29,8 @@ SENTRY_DSN="___PUBLIC_DSN___"
 ###< sentry/sentry-symfony ###
 ```
 
+When using Symfony Flex, the Sentry bundle is configured to be enabled in the `prod` environment only by default. You can change this behaviour in your `config/packages/sentry.yaml` and `config/bundles.php` files.
+
 <Alert level="warning">
   In order to receive stack trace arguments in your errors, make sure to set `zend.exception_ignore_args: Off` in your php.ini
 </Alert>