Currently, config-by-file is bound to registries via the YamlConfigurationSourceBuilder, which requires each module having a registry to build such source, using sensible default for e.g. root path or file name regex pattern.

In this step, we want to make it optional to have file-observation set up.

This should be a separate optional module in main, using Guice multi-bindings for example, to initialize these default config-sources for all registries currently alive in the system.