Add configuration to start external compactions and scan servers

Right now when using uno if I want to start external compactions or scan servers I need to stop accumulo change the cluster.yaml within the install folder and then start accumulo back up. It would be nice to be able to have uno start these services for me.

Start by reading Uno's service-startup flow and the cluster.yaml in the install folder, then trace how external compactions and scan servers are currently configured. Define the configuration entry point and verify that starting Uno enables both services without manually stopping and restarting Accumulo.

Written by the indexing model from the issue text.