Support TensorFlow 2 / Keras

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Is your feature request related to a problem? Please describe.

• Currently, the anomalib only supports pytorch. But there's a huge community who uses tf2/keras. Adding support to the tf2/keras implementation of the anomaly models can serve greatly and cover more anomalib users.

Describe the solution you'd like

• To reduce the boilerplate code of pure tensorflow and reduce the implementation cost, the keras framework can be used.

Describe alternatives you've considered

• Translating the pytorch models into keras. With minimal cost, this is straightforward.

Additional context

• There are many 3rd partly library (for example DocTR for OCR), which supports both frameworks, same code same semantics.