[Core/UX] Add Job API and support managed job (both on-demand and spot) #14402

Job	Run time
python-test (3.8, tests/unit_tests)	3m 58s
python-test (3.8, tests/test_api.py)	3m 45s
python-test (3.8, tests/test_cli.py)	3m 54s
python-test (3.8, tests/test_config.py)	3m 38s
python-test (3.8, tests/test_global_user_state.py)	3m 41s
python-test (3.8, tests/test_jobs.py)	3m 44s
python-test (3.8, tests/test_list_accelerators.py)	3m 52s
python-test (3.8, tests/test_optimizer_dryruns.py)	3m 48s
python-test (3.8, tests/test_optimizer_random_dag.py)	3m 44s
python-test (3.8, tests/test_storage.py)	3m 39s
python-test (3.8, tests/test_wheels.py)	3m 43s
python-test (3.8, tests/test_jobs_and_serve.py)	3m 36s
python-test (3.8, tests/test_yaml_parser.py)	3m 41s
	48m 43s

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