Add support for reading YAML pipeline run files gzipped directly

It seems it is now common to have YAML files for pipeline runs files gzipped. So we could support this transparently in the core package. This is pretty easy:

            with gzip.open(pipeline_run_path, 'rt', encoding='utf8') as pipeline_run_file:
               pipeline_runs = utils.yaml_load_all(pipeline_run_file)