[k8s] Support for switching k8s contexts #16155

Job	Run time
python-test (3.8, tests/unit_tests)	6m 34s
python-test (3.8, tests/test_api.py)	4m 0s
python-test (3.8, tests/test_cli.py)	4m 20s
python-test (3.8, tests/test_config.py)	4m 3s
python-test (3.8, tests/test_global_user_state.py)	3m 54s
python-test (3.8, tests/test_jobs.py)	5m 35s
python-test (3.8, tests/test_list_accelerators.py)	4m 18s
python-test (3.8, tests/test_optimizer_dryruns.py)	5m 45s
python-test (3.8, tests/test_optimizer_random_dag.py)	4m 36s
python-test (3.8, tests/test_storage.py)	4m 9s
python-test (3.8, tests/test_wheels.py)	3m 55s
python-test (3.8, tests/test_jobs_and_serve.py)	3m 53s
python-test (3.8, tests/test_yaml_parser.py)	4m 54s
	59m 56s

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