Support nested args syntax in cmdline

[bouthilx]

An argument such as orion hunt python script.py --nested.arg someprior() would cause a keyerror issue during experiment build:

$ orion -vv hunt -n v0.6 --config=orion.yaml python train.py --optim.lr="orion~loguniform(1e-2, 1e-4)"
2023-01-06 15:37:05,797::DEBUG::orion.core.cli.base::Orion version : 0.2.6
...
Traceback (most recent call last):
  File "/Users/user/.pyenv/versions/3.9.2/bin/orion", line 8, in <module>
    sys.exit(main())
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/cli/__init__.py", line 36, in main
    return orion_parser.execute(argv)
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/cli/base.py", line 110, in execute
    returncode = function(args)
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/cli/hunt.py", line 192, in main
    experiment = experiment_builder.build_from_args(args)
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/io/experiment_builder.py", line 366, in build_from_args
    return builder.build(**cmd_config)
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/io/experiment_builder.py", line 515, in build
    config = self.consolidate_config(name, version, config)
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/io/experiment_builder.py", line 733, in consolidate_config
    resolve_config.update_metadata(config["metadata"])
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/io/resolve_config.py", line 310, in update_metadata
    cmdline_parser.set_state_dict(metadata["parser"])
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/io/orion_cmdline_parser.py", line 134, in set_state_dict
    self.infer_user_script(self.parser.format(self.parser.arguments))
  File "/Users/user/.pyenv/versions/3.9.2/lib/python3.9/site-packages/orion/core/io/cmdline_parser.py", line 109, in format
end(item.format(**configuration))
KeyError: 'nested'

It should be supoprted, just like we support nested arguments in config.