Create JsonConfigLoader.

This CL adds a JsonConfigLoader to parse the vehicle proeprty
config file in JSON format.

This CL also adds DefaultConfigTest to verify the JSON file
is compatible with the existing header file.

Test: atest JsonConfigLoaderUnitTest
atest VehicleHalDefaultConfigTest
Bug: 238685398

Change-Id: If679afd2245cb7e2a49fd964f343b660c9bcea25