Allow setting `merge_with_nonprivate` in `run_experiment.py` command line params

[Dongge Liu]

Changes

Add arg:

fuzzbench/experiment/run_experiment.py

Line 706 in 2bc06d4

 args = parser.parse_args(args) 

pass param:

fuzzbench/experiment/run_experiment.py

Line 743 in 2bc06d4

 start_experiment(args.experiment_name, 

Update config:

fuzzbench/experiment/run_experiment.py

Line 334 in 2bc06d4

 config['runner_num_cpu_cores'] = config.get('runner_num_cpu_cores', 1) 

Reference links

It takes config file at:
https://github.com/google/fuzzbench/blob/2bc06d4aca2c8dae20eeca47b95433ef543f99a8/experiment/run_experiment.py#L180C10-L180C31