Fine tune model based on TimeGPT

[Imortalco]

Read about :

• [ ] - Exogenous variables
• [x] - finetune_steps param in forecast method
• [x] - Fine-tuning with a specific loss function
• [ ] - Anomaly detection

[Imortalco]

Added fine tune stapes and specific loss function ('mae'). Next step is probably to add hyperparameter tuning. IDK