Support handle-as for metadata properties

[angelozerr]

Properties collection follow the same format than https://docs.spring.io/spring-boot/docs/current/reference/html/appendix-configuration-metadata.html

It should be fine to support handle-as to say for instance that some quarkus property have log level enumeration although the property is a string.

It will allog to remove the ugly https://github.com/eclipse/lsp4mp/blob/master/microprofile.ls/org.eclipse.lsp4mp.ls/src/main/resources/org/eclipse/lsp4mp/model/values/quarkus-values-rules.json

[angelozerr]

Fixed with #105