This can be used to extract embedded configurations for other plugins out
of larger (parent) configurations.

A example where this can be useful is plugin bundles (see the
Config::MVP::Assembler::WithBundles manpage).

A bundle loads other plugins with a default configuration that works most
of the time, but sometimes you wish you could customize the configuration
for one of those plugins without having to remove the plugin from the
bundle and re-specify it separately.