Curator ingest_envoy fix

This fixes a bug, sorry I didn't catch it during the MR review.

IngestionManifest.init() wants a Path for non-curator ingestion or None for curator's, but curation_source was being passed as a string. IngestionManifest thought it had a staging_source_dir when it shouldn't have and was trying to call iterDir() on a string which threw an exception.

If you're curious, this exception can be found at /lustre/aoc/cluster/pipeline/dsoc-dev/workspaces/spool/tmpx1d6k8xv/curator.err

File "/tmp/tmph47b5pgr/installed_wheels/cb7f233d496f934849e4e78eadba0b5457afd412cb8116dcab03401ba89d8a84/ingest_envoy-2.8.2.1rc1-py3-none-any.whl/ingest_envoy/ingestion_manifest.py", line 103, in __init__
    self.files_found = [file for file in self.staging_source_dir.iterdir()]
AttributeError: 'str' object has no attribute 'iterdir'