Reread config file after startup

[gothub]

metadig-engine apps read the configuration file metadig.properties at app startup. If the configuration file is changed after the app starts, it is not re-read.

Update all apps (metadig-controller, metadig-worker, metadig-scorer, metadig-scheduler) to reread the config file if it is updated after startup. One approach to achieve this is described here. This approach works in a k8s environment, where the config file is mounted as a volume, as shown in the metadig-controller deployment.