[FSDP] Make env var and dataclass flag consistent for cpu_ram_efficient_loading

[SumanthRH]

What does this PR do?

Makes environment variable and dataclass consistent for cpu_ram_efficient_loading. Currently, there's an inconsistency when the FSDP plugin is initialized in a standalone fashion: the cpu_ram_efficient_loading flag can be set to True but if the user doesn't use accelerate launch , then the environment variable FSDP_CPU_RAM_EFFICIENT_LOADING would not be set. This environment variable is actually used by transformers to initialize parameters efficiently in the process group (See: #2100 (comment) for details on how this happens)

I can see a previous PR #2998 that tried to make all env vars optional, but looks like this was left.

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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cc @muellerzr

[HuggingFaceDocBuilderDev]

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[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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[SumanthRH]

not stale

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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[SumanthRH]

not stale.

@muellerzr would appreciate a review on this!

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the contributing guidelines are likely to be ignored.

[SumanthRH]

not stale

[SunMarc]

cc @S1ro1 if you can take a look as you were working on that for fsdpv2 also

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the contributing guidelines are likely to be ignored.

[S1ro1]

not stale, gonna take a look!