Upload file with metadata

Upload a file using multipart/form-data with metadata. Returns an object_id for the uploaded file and submission_id for the metadata submission.

Example:

curl -k -u n:n -F "file=@example.txt"          -F 'metadata={"agent_id":"agent123","project":"proj1","timestamp":"2024-01-29T12:00:00Z","expiration":"2024-02-29T12:00:00Z","path":"/tmp/example.txt"}'          https://nemesis:7443/api/files