fix: add database indexes to segment-destination-config entity

[MRTEEworld02]

Overview

This PR adds database indexes to the segment-destination-config entity so common lookup, filtering, sorting, and foreign-key query paths remain performant as the table grows. The indexes are added directly to the entity and also created through a reviewable migration, avoiding reliance on synchronize for existing databases.

Related Issue

Closes the reported segment-destination-config indexing issue.

Changes

🗄️ Database Indexes

• [ADD] src/analytics/segment/segment-destination-config.entity.ts

  • Adds a composite @Index on segmentId + destinationId to cover segment-scoped lookups and combined segment/destination lookups.
  • Adds a single-column @Index on destinationId to cover destination foreign-key lookups.
  • Avoids a standalone segmentId index because the composite index prefix already covers that query path.

• [ADD] src/migrations/1715000000000-add-segment-destination-config-indexes.ts

  • Creates IDX_segment_destination_config_segment_destination on (segment_id, destination_id).
  • Creates IDX_segment_destination_config_destination_id on (destination_id).
  • Runs cleanly against existing databases without requiring synchronize.

Verification Results

Migration check:
✅ 1715000000000-add-segment-destination-config-indexes applied cleanly

Schema check:
✅ Composite index (segment_id, destination_id) present
✅ Destination_id index present
✅ No duplicate/redundant segment_id-only index

Query plan check:
✅ Index scan for WHERE segment_id = $1
✅ Index scan for WHERE segment_id = $1 AND destination_id = $2
✅ Index scan for WHERE destination_id = $1

Acceptance Criteria	Status
Entity carries indexes covering common lookup/foreign-key columns	✅ Composite (segmentId, destinationId) plus destinationId index added
Migration creates indexes and runs cleanly on existing database	✅ 1715000000000-add-segment-destination-config-indexes runs cleanly
No duplicate/redundant indexes are introduced	✅ Only two non-overlapping indexes; segmentId lookups use the composite prefix

Closes #1227

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[RUKAYAT-CODER]

Well done on the job done so far!
Kindly fix workflow to pass