Introduce support for npm packages

Currently, the extensionId field of DocApp.Code.DocumentationExtensionClass expects a maven module reference (e.g., org.xwiki.platform:xwiki-platform-application-ui)

This field is used to generate a link to the page of the corresponding extension in the https://extensions.xwiki.org (https://www.xwiki.org/xwiki/bin/view/documentation/extensions/user/documentation/documentation-xwiki-org/page-structure-xwikiorg/).

Now that we are also publishing npm packages, it could be interesting to support npm package IDs as well (possibly with improvements on the extension application).