FEAT: Update Status Of Video Row On Media Convert Update

cms/internal/db/migrations/0003_index_videos_mediaconvert_job_id.down.sql

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+DROP INDEX videos_mediaconvert_job_id_idx;

cms/internal/db/migrations/0003_index_videos_mediaconvert_job_id.up.sql

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+-- Job state changes arrive keyed by MediaConvert's job id, so every event the
+-- consumer handles is a lookup on this column. Nothing indexed it before: the
+-- column was only ever written, never searched.
+CREATE INDEX videos_mediaconvert_job_id_idx ON videos (mediaconvert_job_id);