Adds rake task "polls:remove_duplicate_partial_results" to delete duplicated
rows in "poll_partial_results" made before the DB was strict about duplicates.
Duplicates are considered only for records without "option_id", grouping by:
(question_id, booth_assignment_id, date, answer). We keep the first one and
delete the rest, per tenant.
The controller use:
Poll::PartialResult.find_or_initialize_by(booth_assignment_id, date, question_id, answer)
which is not a strong protection against race conditions. Without a unique
index at the DB level, duplicates could be created. This task cleans up any
existing duplicates.
e286ee6943