Docs: Document the addition of `$json_report_pathname` parameter to the...

Docs: Document the addition of `$json_report_pathname` parameter to the `wp_privacy_personal_data_export_file_created` action.

Follow-up to [47146].

Props xkon.
Fixes #49029.
Built from https://develop.svn.wordpress.org/trunk@47150


git-svn-id: https://core.svn.wordpress.org/trunk@46950 1a063a9b-81f0-0310-95a4-ce76da25c4cd