We need the same ability (as Google Sign Builder) to consume a configuration file associated with our custom extension -- but I read that the extension needs to be capable of doing so first, before the Admin Console UI provides an option to upload.
See: Chrome Policies and click its "Install custom policies for an app" section for the console's UI example I reference above.
I see mentions here of a managed_schema entry in the extension's manifest.json -- I cannot find any references to this attribute nor any working example of such a thing. Can someone provide one here please?
Our Google Admin for Business support re-directed me here to ask this developer community.
Feel free to review this extension's source code