QAT to PTQ documentation update

[daniil-lyakhov]

Details:

QAT documentation for NNCF Torch and NNCF Tensorflow is spitted on two pages

• quantization-aware-training-pytorch.rst is QAT by nncf.quantize method documentation
• quantization-aware-training-tensorflow.rst file is a copy of original quantization-aware-training.rst without the PyTorch part New structure:

Tickets:

• 129586