Deprecate warmup_ratio

[SunMarc]

What does this PR do?

This PR deprecates warmup_ratio. Instead we ask the user to use warmup_steps instead as we now allow passing float values. This is something that was already done for a few args like eval_steps .

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[qgallouedec]

we use warmup_ratio a lot in our recipes/configs, but when I think about it, it might make more sense to use warmup_step instead., I'd be curious to hear the feedback of @edbeeching @lewtun on this.

[SunMarc]

we use warmup_ratio a lot in our recipes/configs, but when I think about it, it might make more sense to use warmup_step instead., I'd be curious to hear the feedback of @edbeeching @lewtun on this.

I don't mind keeping it if you think this will lead to too many complications !