Adding CLS token back to Eva Transformer

[surajpaib]

dynamic-network-architectures/dynamic_network_architectures/building_blocks/eva.py

Line 62 in 6d9f47e

- self.cls_token removed

It would be great to have the CLS token added back to the Eva Transformer and could be done conditionally based on a flag in the class def. https://docs.monai.io/en/1.3.0/_modules/monai/networks/nets/vit.html

Reason: Making Eva (and Primus by extension) compatible for pretraining with DINOv2 and for classification in general.