Add newline after comments in rush.json (#17912)

to make it easier to `grep -v` comment lines and get valid json.

rush.json

@@ -1,7 +1,8 @@
 /**
  * This is the main configuration file for Rush.
  * For full documentation, please see https://rushjs.io
- */{
+ */
+{
   "$schema": "https://developer.microsoft.com/json-schemas/rush/v5/rush.schema.json",
   /**
    * (Required) This specifies the version of the Rush engine to be used in this repo.