Auto start root datastore for gc sweep test

[tyler-cai-microsoft]

Part of AB#1847 and AB#1837

As a part of https://github.com/microsoft/FluidFramework/pull/11928/files#

The RootDataObjectWithChildDataObject should be generating ops and then referencing and unreferencing its child datastore as soon as it is initialized. This should repeat until the container closes, or the test ends.