Officially deprecate legacy `GET /query` endpoint for `POST /subjects`

[alyssadai]

• Remove OPTIONAL statement for dataset_portal_uri (only needed for backwards compatibility) from cohort query template (create_query):

  OPTIONAL {{?dataset_uuid nb:hasAccessLink ?dataset_portal_uri.}}

• Update or remove test fixture mock_post_nonagg_query_to_graph since we will no longer return dataset metadata for a cohort query

[Tusharjamdade]

Hi @alyssadai,
I’d be happy to take this up, please let me know if you’d like me to work on this.

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