[Test][Autoscaling] Add custom resource test

[MortalHappiness]

Why are these changes needed?

This is a subtask for the umbrella issue #2173

Related issue number

See #2173 for details

Checks

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