This task of adding a custom processor to read data from a JSON file requires some software development work. It requires you to build a customized version of Winlogbeat. The developer guide is helpful to show how to build a beat, but it doesn't go into processors (for that use the existing ones as a guide).
If you aren't up for development then please open an enhancement request for a new "add_json_metadata" processor in the project's repo on Github.