[Core/UX] Add Job API and support managed job (both on-demand and spot) #14399

Job	Run time
python-test (3.8, tests/unit_tests)	6m 56s
python-test (3.8, tests/test_api.py)	4m 1s
python-test (3.8, tests/test_cli.py)	4m 15s
python-test (3.8, tests/test_config.py)	3m 39s
python-test (3.8, tests/test_global_user_state.py)	4m 1s
python-test (3.8, tests/test_jobs.py)	4m 19s
python-test (3.8, tests/test_list_accelerators.py)	4m 12s
python-test (3.8, tests/test_optimizer_dryruns.py)	5m 26s
python-test (3.8, tests/test_optimizer_random_dag.py)	4m 42s
python-test (3.8, tests/test_storage.py)	3m 47s
python-test (3.8, tests/test_wheels.py)	3m 52s
python-test (3.8, tests/test_jobs_and_serve.py)	3m 56s
python-test (3.8, tests/test_yaml_parser.py)	3m 50s
	56m 56s

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