Modular can be configured through a JSON file that is packaged through modular_config().
modular_config.gni defines the build rule that does the following:
- Validates the client provided configuration against modular_config_schema.json.
- Adds the client provided configuration to basemgr's /config/data.
- Adds basemgr.config to sysmgr's /config/data. This tells sysmgr to launch basemgr whenever a package created by modular_config() has been included in a device image.