Improve deepspeed env gen

[muellerzr]

What does this PR do?

This PR improves the deepspeed env file generation by making sure any bad flags include a warning that they are being strict.

Avoid trailing newline and avoid writing some other characters that would break reading in this file.

DeepSpeed [code](https://github.com/microsoft/DeepSpeed/blob/688239e3f24f7ba11d3fe90bbe9670b7a61e5440/deepspeed/launcher/runner.py#L560) that reads from this file is naive and thus requires strict narrowing of legal key=value lines.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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@pacman100

[HuggingFaceDocBuilderDev]

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[pacman100]

Thank you @muellerzr for the fixes and the test!

[muellerzr]

I chose to not include = as in their official guide they recommend setting it in the .env variable using =