Allow boolean FSDP options in fsdp_config

[helloworld1]

What does this PR do?

When using the fsdp_config option, it must be passed in as string for some configuration.
The following config will result in crash

{
  "limit_all_gathers": true,
  "backward_prefetch": "backward_pre",
  "use_orig_params": true,
  "cpu_ram_efficient_loading": true
}

Error:

Traceback (most recent call last):
  File "/home/jobuser/training.py", line 107, in <module>
    main()
  File "/home/jobuser/training.py", line 40, in main
    training_args, custom_args = parser.parse_args_into_dataclasses()
  File "/home/jobuser/.local/lib/python3.10/site-packages/transformers/hf_argparser.py", line 338, in parse_args_into_dataclasses
    obj = dtype(**inputs)
  File "<string>", line 121, in __init__
  File "/home/jobuser/.local/lib/python3.10/site-packages/transformers/training_args.py", line 1691, in __post_init__
    os.environ[f"{prefix}USE_ORIG_PARAMS"] = self.fsdp_config.get("use_orig_params", "true")
  File "/export/apps/python/3.10/lib/python3.10/os.py", line 684, in __setitem__
    value = self.encodevalue(value)
  File "/export/apps/python/3.10/lib/python3.10/os.py", line 756, in encode
    raise TypeError("str expected, not %s" % type(value).__name__)
TypeError: str expected, not bool

This PR fixed the issue by casting the config value to str.

Fixes # (issue)

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Who can review?

@pacman100 @muellerzr @amyeroberts

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[muellerzr]

This looks like an okay change to me, however just to be extra careful, let's do a .lower() as well please :)

[HuggingFaceDocBuilderDev]

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[pacman100]

Thank you @helloworld1 for fixing this!

[amyeroberts]

Thanks for fixing!