[Core/UX] Add Job API and support managed job (both on-demand and spot) #14403

Job	Run time
python-test (3.8, tests/unit_tests)	1m 34s
python-test (3.8, tests/test_api.py)	4m 1s
python-test (3.8, tests/test_cli.py)	4m 10s
python-test (3.8, tests/test_config.py)	3m 34s
python-test (3.8, tests/test_global_user_state.py)	3m 42s
python-test (3.8, tests/test_jobs.py)	1m 45s
python-test (3.8, tests/test_list_accelerators.py)	1m 40s
python-test (3.8, tests/test_optimizer_dryruns.py)	1m 39s
python-test (3.8, tests/test_optimizer_random_dag.py)	1m 40s
python-test (3.8, tests/test_storage.py)	1m 40s
python-test (3.8, tests/test_wheels.py)	1m 34s
python-test (3.8, tests/test_jobs_and_serve.py)	3m 39s
python-test (3.8, tests/test_yaml_parser.py)	1m 36s
	32m 14s

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