BootstrapNAS: Export best subnet to onnx

[jpablomch]

Changes

Add calls in examples to export the resulting best subnet to ONNX

Reason for changes

Example of exporting to ONNX requested by user.

Related tickets

N/A

Tests

Test for exporting to ONNX are already included in test suite.

[jpablomch]

@ljaljushkin Please take a look. Thanks!

[ljaljushkin]

This PR can't be merged without passing all pre-commit checks.

There's issue with code style, please refer to pylint check log.

Also, one e2e test for efficient (nas.test_sanity_sample.test_e2e_supernet_training[efficient_net_b1_cifar10_nas.json_classification_nas_mock_32x32]) is failing with error: RuntimeError: ONNX export failed: Couldn't export Python operator SwishImplementation.

Seems like there's an option to use export-friendly version of this model: https://github.com/lukemelas/EfficientNet-PyTorch/issues/91#issuecomment-542994572 Please use that version in the test.

[openvino-nncf-ci]

Can one of the admins verify this patch?

[aiarkinx]

run build

[jpablomch]

run build

[jpablomch]

run build

[jpablomch]

run build

[jpablomch]

run build