[Core/UX] Add Job API and support managed job (both on-demand and spot) #14395

Job	Run time
python-test (3.8, tests/unit_tests)	6m 16s
python-test (3.8, tests/test_api.py)	3m 55s
python-test (3.8, tests/test_cli.py)	4m 17s
python-test (3.8, tests/test_config.py)	4m 15s
python-test (3.8, tests/test_global_user_state.py)	3m 40s
python-test (3.8, tests/test_jobs.py)	4m 4s
python-test (3.8, tests/test_list_accelerators.py)	4m 0s
python-test (3.8, tests/test_optimizer_dryruns.py)	5m 27s
python-test (3.8, tests/test_optimizer_random_dag.py)	4m 11s
python-test (3.8, tests/test_storage.py)	3m 35s
python-test (3.8, tests/test_wheels.py)	3m 46s
python-test (3.8, tests/test_jobs_and_serve.py)	3m 42s
python-test (3.8, tests/test_yaml_parser.py)	3m 44s
	54m 52s

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