Add a BND plugin to the scriptingbundle-maven-plugin

To directly enrich the Manifest instead just creating new project properties, the functionality should be embedded in a Bnd plugin like we already have for Sling Models at https://github.com/apache/sling-org-apache-sling-bnd-models/blob/master/src/main/java/org/apache/sling/bnd/models/ModelsScannerPlugin.java.

I don't see a need to keep this as dedicated Maven plugin as all bundle plugins are based on Bnd AFAIK.