Add training, data loading, and dataset configuration to GTCRN

[qianjr2002]

Added train.py to enable model training directly within the repository.

[Xiaobin-Rong]

@qianjr2002 Thank you so much for your contribution! I do apologize if this may seem a bit inconvenient, but this repository does not need training codes as they are available in another repository named 'SEtrain', as indicated in the README.md