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

This MR addresses bug in additional_metadata section of manifest that has a class repr rather than a JSON-serializable value

• tests dump all JSON strings; if dumps succeed, the JSON is good
• removed contrived test case
• added test case based on what an image ingestion staging dir is likely to contain

TODO next MR: implement additional tests for new image ingestion test case

apps/cli/executables/pexable/ingest_envoy/ingest_envoy/collectors.py

-import glob
-import os
-import pathlib
 import shutil
 import subprocess
 import sys
 
 import logging
 
-import json
-
 from ingest_envoy.schema import AbstractTextFile
 
 
@@ -17,6 +12,9 @@ class ImageCollector:
         self.logger = logging.getLogger("ingest_envoy")
         self.parameters = parameters
         self.spl = parameters["spl"]
+        self.staging_source_dir = (
+            self.parameters["staging_area"] + "/" + self.parameters["workflowDir"]
+        )
 
     def collect_image_metadata(self) -> AbstractTextFile:
         file = open("./aux_image_metadata.json", "r")
@@ -34,6 +32,13 @@ class ImageCollector:
             stdout=sys.stdout,
             stderr=sys.stderr,
         )
+        self.aux_file_to_staging()
+
+    def aux_file_to_staging(self):
+        shutil.copy2(
+            "./aux_image_metadata.json",
+            self.staging_source_dir,
+        )
 
     def create_artifacts_name(self):
         name = "pipeline_artifacts_"