What does this PR do?

Fixes a flaky test caused by hardcoded booking UIDs in seated event slot e2e tests. The tests used booking-uid-${seatedEventTypeId} as the UID, which is deterministic and causes Unique constraint failed on the fields: (uid) errors when prior test data isn't fully cleaned up.

Replaces the deterministic ID with randomString() (already imported and used elsewhere in both files) to guarantee uniqueness across runs.

Affected tests:

• slots-2024-04-15/controllers/slots.controller.e2e-spec.ts — 2 occurrences
• slots-2024-09-04/controllers/e2e/user-event-type-slots.controller.e2e-spec.ts — 2 occurrences

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

Run the affected e2e test suites multiple times in succession — the seated event booking tests should no longer fail with unique constraint errors:

yarn test -- src/modules/slots/slots-2024-04-15/controllers/slots.controller.e2e-spec.ts
yarn test -- src/modules/slots/slots-2024-09-04/controllers/e2e/user-event-type-slots.controller.e2e-spec.ts

Human Review Checklist

• Verify randomString() is already imported in both test files (no new dependencies)
• Verify downstream assertions using booking.uid (e.g., bookingUid: booking.uid) still work since they read the value back from the created object

Link to Devin run: https://app.devin.ai/sessions/2741867580d6485c94097e64d3b3b175
Requested by: @alishaz-polymath