add python client

[akanso]

Why are these changes needed?

Today we can create/update/delete rayclusters using kubectl, helm, etc. with yaml/JSON manifests describing the raycluster.

A Python library that can programmatically manage rayclusters (using kuberay) will enable Python applications running on top of Ray and using KubeRay to add/remove/update worker-groups on the fly.

This library enables the application itself to scale the worker-groups horizontally and vertically.

Use case
Two main use cases:

1- Enable a Python application to programmatically manage rayclusters (using kuberay) without the need to deal with YAML/JSON files.

2- We can use this KubeRay Python Client Library in our tests (E2E/Integration) to manage rayclusters without having to run kubectl command from our tests that are written in Python

Related issue number

ray-project#899

Checks

This PR include its own test files with 88% test coverage.

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

python -m coverage report
Name                                                                                                                  Stmts   Miss  Cover
-----------------------------------------------------------------------------------------------------------------------------------------
/home/azureuser/go-code/src/github.com/kuberay/clients/python-client/python_client/constants.py                           6      0   100%
/home/azureuser/go-code/src/github.com/kuberay/clients/python-client/python_client/utils/__init__.py                      0      0   100%
/home/azureuser/go-code/src/github.com/kuberay/clients/python-client/python_client/utils/kuberay_cluster_builder.py      72      9    88%
/home/azureuser/go-code/src/github.com/kuberay/clients/python-client/python_client/utils/kuberay_cluster_utils.py       146     28    81%
test_director.py                                                                                                         74      0   100%
test_utils.py                                                                                                            89      9    90%
-----------------------------------------------------------------------------------------------------------------------------------------
TOTAL                                                                                                                   387     46    88%