Update generic_parser from_json return after ingestion

[EddieLF]

This change makes the generic_parser.from_json function return the full response it receives from Metamist.

When the parser is used to ingest from a manifest, the parser is instantiated:

parser = GenericParser(
    project=dataset,
    search_paths=search_paths,
)

We then call parser.from_manifest_path

response = await parser.from_manifest_path(manifest=manifest_path, dry_run=dry_run)

This returns parser.parse_manifest, which in turn returns parser.from_json. Currently, from_json has no returned value unless the --dry-run flag is set.
This means that nothing can be done to analyse the response beyond what gets logged by the generic parser.

response = await parser.from_manifest_path(manifest=manifest_path, dry_run=dry_run)
print(response)
>>> None

By adding a return result to from_json, the result/response can be printed or analysed by any custom parser implementation.

response = await parser.from_manifest_path(manifest=manifest_path, dry_run=dry_run)
print(json.dumps(response, indent=2))
>>> { Actual JSON response }

[illusional]

Seems sensible!