Add Validator SPI targeted towards OSGi configurations

OSGi configurations in content packages are only supported via the Sling OSGi Installer. That supports multiple different serialization formats. In order to ease implementing validators for OSGi configurations there should be a dedicated SPI class in https://jackrabbit.apache.org/filevault/apidocs/org/apache/jackrabbit/vault/validation/spi/package-summary.html.
That should encapsulate detecting serialized OSGi configurations in a content package and deserialize those into Dictionary as used in https://docs.osgi.org/javadoc/osgi.cmpn/8.0.0/org/osgi/service/cm/Configuration.html#getProperties--