WS-601: 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:
additional tests for new image ingestion test case

* EVLA CAL manifest example updated
* manifest filename now `ingestion-manifest.json`
* EVLA CAL ingestion artifacts file contains only the manifest
* 1500 new grey hairs added to Janet's head

TODO next MR:
* yet more fixing of broken tests and implementation of TODO tests*

`await-qa` step

TODO: fix or remove each of the disabled tests