wrap research_data row addition in critical section

[pbugni]

wrap research_data row addition in critical section, keyed on unique constraint, as we do rarely experience asynchronous collisions.

this is intended to prevent exceptions such as the following, seen once during the initial population of 100K rows:

Unexpected exception in `cache_research_data_task` on 231 : (psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint "ix_research_data_questionnaire_response_id"
DETAIL:  Key (questionnaire_response_id)=(97480) already exists.