ResNet support

Resnet is supported by decavision according to the docstring of the `ImageClassifier` class and has seen in the code [here](https://github.com/Decathlon/decavision/blob/master/decavision/model_training/tfrecords_image_classifier.py#L254).

However, Resnet seems to be missing from the dict of [input_dims](https://github.com/Decathlon/decavision/blob/master/decavision/model_training/tfrecords_image_classifier.py#L100)

Read decavision/model_training/tfrecords_image_classifier.py, especially the input_dims dictionary around line 100 and the ResNet-related path around line 254. Confirm how ResNet is selected and what dimensions it requires; done means the supported ResNet model has a matching input_dims entry and the existing classifier path can use it.

Written by the indexing model from the issue text.