Add support for a new annotation, @GrabMetadata, that can be used
to provide the coordinates of one or more properties files, such as
the one published by Spring IO Platform, as a source of dependency
metadata. For example:
@GrabMetadata("com.example:metadata:1.0.0")
The referenced properties files must be in the format
group:module=version.
Limitations:
- Only a single @GrabMetadata annotation is supported
- The referenced properties file must be accessible in one of the
default repositories, i.e. it cannot be accessed in a repository
that's added using @GrabResolver
Closes#814
d2fc80b818