Fix SOMA ingestion's registration race condition.

[JohnMoutafis]

Issue

The SOMA ingest creates a taskgraph called launcher (run_ingest_workflow_udf) that creates the h5ad ingestor task and calls compute on that graph.
That creates a race condition with the ingested SOMA Group registration (initiated from the ingest graph) that results in an empty SOMA although every node of the graph resolves without failures, or in another case in a registration failure (manual registration of that Group showed that the ingestion process was resolved correctly).

Solution

Move the registration inside the launcher process.

[sgillies]

Thanks for the analysis and description @JohnMoutafis !