Universal Agent bundle

At the moment we ship bundles per Spark+Scala version pair. But currently and apparently the only reason we still need separate Spark bundles is the `json4s-ext` dependency that is linked with the `json4s-core` that is a part of the Spark runtime and is not binary compatible across different Spark versions. If we replace it with something else we could potentially get of bundles per Spark version. So we would only have two ones per Scala version.