Add support for PHP to beforeSendTransaction

Author: cleptric

src/platforms/common/configuration/options.mdx

@@ -567,7 +567,7 @@ This function is called with an SDK-specific message or error event object, and
 
 </ConfigKey>
 
-<ConfigKey name="before-send-transaction" supported={["javascript", "node"]}>
+<ConfigKey name="before-send-transaction" supported={["javascript", "node", "php"]}>
 
 This function is called with an SDK-specific transaction event object, and can return a modified transaction event object, or `null` to skip reporting the event. This can be used, for instance, for manual PII stripping before sending.