Create the FSDP Plugin in the trainer explicitly rather wait for it to be setup by accelerate

[winglian]

What does this PR do?

See the corresponding PR here huggingface/accelerate#3033. Ultimately I want to see device_mesh support, but this brings the fsdp_plugin to parity with the deepspeed plugin in training args.

@ArthurZucker @muellerzr

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This is the corresponding PR to huggingface/accelerate#3033 that will enable passing a device_mesh

[HuggingFaceDocBuilderDev]

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