Add --revision to optimum-cli export openvino

[helena-intel]

Add --revision option to optimum-cli export openvino.

TODO:

• this PR does not include loading preprocessors from a revision, because for that maybe_load_preprocessors from optimum is used, which does not support a revision argument. @echarlaix / @IlyasMoutawwakil would appreciate your input on how to handle this.
• add to documentation

I wanted to add a better test but did not see a way to check the revision of the model after it has been converted. If there is a tiny model where a new revision for example only makes a non-breaking change to the model config I could use that and check for the expected config in the test. I could also duplicate an existing tiny model to do that.

Unrelated changes are from formatting with black.

[HuggingFaceDocBuilderDev]

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[echarlaix]

Looks good thanks @helena-intel !

I wanted to add a better test but did not see a way to check the revision of the model after it has been converted.

You should be able to check the model's config._commit_hash to check for the commit id. You could also potentially add a test with a tiny model by specifying a branch name directly to make sure this also works as well