SSP controller: avoid expensive subqueries

[irees]

Using operator_onestop_id calls Operator.find_by_onestop_ids!

    operators = Operator.find_by_onestop_ids!(AllowFiltering.param_as_array(params, :operator_onestop_id))
    @ssps = @ssps.where(operator: operators)

which produces a query using a subquery to find operators:

SELECT  "current_schedule_stop_pairs".* FROM "current_schedule_stop_pairs" WHERE "current_schedule_stop_pairs"."operator_id" IN (SELECT id FROM "current_operators" WHERE "current_operators"."onestop_id" = 'o-123-81')  ORDER BY "current_schedule_stop_pairs"."id" ASC LIMIT 51 OFFSET 0

This is very expensive and can timeout.

Using pluck on Operator.find_by_onestop_ids! (at the cost of a second query) produces a simpler, more efficient, more index-searchable form for the main query:

SELECT  "current_schedule_stop_pairs".* FROM "current_schedule_stop_pairs" WHERE "current_schedule_stop_pairs"."operator_id" = 1  ORDER BY "current_schedule_stop_pairs"."id" ASC LIMIT 51 OFFSET 0

Use this form in all SSP query params, and consider expanding to all controllers.