WS-601: addresses bug in additional_metadata section of image manifest

...s/pexable/ingest_envoy/ingest_envoy/ingestion_manifest.py

...xable/ingest_envoy/ingest_envoy/std_img_manifest_utils.py

apps/cli/executables/pexable/ingest_envoy/test/conftest.py

...ngest_envoy/test/examples/image_manifest_tmpx_ratuqh.json

...cutables/pexable/ingest_envoy/test/test_image_manifest.py

...es/pexable/ingest_envoy/test/test_img_manifest_example.py

...e/ingest_envoy/test/test_manifest_builder_entry_points.py