Provide custom properties mapping in the metadata

[snicoll]

Whenever we offer links to the end user, those should eventually match the generation of Spring Boot that you have chosen.

This works fine for Spring Boot as the remote clients can just use that information. However, we have no way to communicate other versions to the user. For instance if we manage the mapping of a library, it would nice that the link to the doc matches the actual version according to the chosen Spring Boot generation.

In the case of Spring Cloud, things are getting much harder as there isn't a consolidated doc per release train. Ideally, we should have links with the release train version in the URL rather than the versions of the individual components as such version isn't exposed to us at the moment.