Refactor request for total number of subjects in matching datasets into separate function

[alyssadai]

This separate request is currently hard to mock b/c it uses the same functions as the primary phenotypic query

api/app/api/crud.py

Lines 133 to 143 in 34ea1fc

	matching_dataset_size_results = post_query_to_graph(
	util.create_multidataset_size_query(
	results_df["dataset_uuid"].unique()
	)
	)
	matching_dataset_sizes = {
	ds["dataset_uuid"]: int(ds["total_subjects"])
	for ds in util.unpack_http_response_json_to_dicts(
	matching_dataset_size_results
	)
	}