chore(aci): add unique together constraint on DetectorWorkflow

[ameliahsu]

each detector-workflow pair should only have 1 connection

[cathteng]

should we add this constraint for all the workflow engine lookup tables?

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/workflow_engine/migrations/0038_add_detector_workflow_unique_together.py ()

--
-- Alter unique_together for detectorworkflow (1 constraint(s))
--
CREATE UNIQUE INDEX CONCURRENTLY "workflow_engine_detector_detector_id_workflow_id_e900662b_uniq" ON "workflow_engine_detectorworkflow" ("detector_id", "workflow_id");
ALTER TABLE "workflow_engine_detectorworkflow" ADD CONSTRAINT "workflow_engine_detector_detector_id_workflow_id_e900662b_uniq" UNIQUE USING INDEX "workflow_engine_detector_detector_id_workflow_id_e900662b_uniq";

[saponifi3d]

@cathteng - agree, but we should probably enumerate a list and just knock them all out in a separate PR -- this can at least unblock @ameliahsu on the API she's building.

[saponifi3d]

LGTM - i think you might need a DB migration +1 as well though.