Add ZeRO++ to DeepSpeed usage docs

[SumanthRH]

What does this PR do?

A long pending follow-up to issue #2020. This PR adds ZeRO++ to the DeepSpeed usage guide. I've also made some minor edits to clarify that all features of the ZeRO protocol are supported.

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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• Did you write any new necessary tests?

Who can review?

@muellerzr

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[pacman100]

Thank you @SumanthRH for updating the DeepSpeed documentation to highlight the support for the ZeRO++ features such as Hybrid Sharding and weight quantization during communication operations to reduce the communication volume. LGTM! 🚀