Allow using system properties to fill up the template value in configs.

Current pinot supports environment variables override for table config template. We should also add the support and convention for system properties, as that is much simpler to use and set during runtime.

Start by locating the existing environment-variable override for table config templates and trace how template values are resolved. Determine the project’s convention for runtime system properties, then add equivalent support and verify that system properties populate template values without breaking environment-variable behavior.

Written by the indexing model from the issue text.