Migrate metric to Evaluate in Pytorch examples

[atturaioe]

What does this PR do?

As metrics are being deprecated in Datasets, they need to be moved to Evaluate. This PR migrates function calls of load_metric from Datasets to load in Evaluate in Pytorch examples.

Fixes #18306

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@sgugger

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Perfect, thanks a lot for your work on this!