Add extension components metadata for all script services exposed

Many core modules provide services API today for developers to be able to use XWiki programatically.

In order to be able to connect extensions documentation with the services they document (mainly, but other usages are possible), all the modules of the XWiki platform that do so should declare the ScriptService components they provide as custom properties in their poms https://extensions.xwiki.org/xwiki/bin/view/Extension/Extension%20Module/Repositories/Maven/#HCustomproperties .

This would then allow to extract the services from an extension / extension repository, and, using extensions.xwiki.org, tie a documentation to the service it documents.