added autoscaling support to Python APIs

[blublinsky]

@tedhtchang, @smit-kiri, @anyscalesam

Why are these changes needed?

This cleans up Python implementation add support for creation of autoscaling clusters and image pull policy

Related issue number

https://github.com/ray-project/kuberay/issues/2029

Checks

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

[blublinsky]

@tedhtchang, @smit-kiri, @anyscalesam, please take a look

cc @kevin85421

[smit-kiri]

Just a general suggestion on the classes defined here - most of them could be defined as dataclass objects. Makes it easier to read / know types of the fields

[blublinsky]

@kevin85421 all yours