Add finalizer to worker pods to ensure min replica

[YichengWang12]

Why are these changes needed?

Currently all worker pods can be deleted without protection, regardless of minReplica. This change adds a protection of minReplica using finalizer.

Related issue number

Fix #1740

Checks

• [ ] I've made sure the tests are passing.
• Testing Strategy
  • [ ] Unit tests
  • [ ] Manual tests
  • [ ] This PR is not tested :(