Add a new `spring-boot-configuration-metadata` module that provides an
API to manipulate Spring Boot configuration meta-data. Can read meta-data
from arbitrary locations, though the standard
`META-INF/spring-configuration-metadata.json` location must be preferred.
Closes gh-1970
Add a companion module that IDE developers can use to read configuration
metadata from multiple sources into a single repository.
ConfigurationMetadataRepository provides access to groups and items as
well as an harmonized view on "sources" (that is the POJOs that have
contributed to a given group).
Closes gh-1970
