Support gzipped QCOW2 images and document the supported inputs of a pipeline

QCOW2 images may be gzipped as foo.qcow2.gz and it would be nice to allow and accept input that are gzipped or tar gzipped as inputs to the `analyze_root_filesystem_or_vm_image` pipeline

In all cases, we should document which input we accept for this pipeline and in general it would be nice to have a docstring-like in each pipeline that tells what are the expected input formats.