Implement TogetherAI and Flux Image Generation

[soymh]

Happy New Year to the great team of this incredible project!

This PR introduces initial support for TogetherAI models and Flux Image generation. The changes are still in the early stages, but I wanted to share the progress and get feedback from the community.

Changes:

• Added support for TogetherAI models
• Implemented Flux Image generation

Notes:
Please review and let me know if there's anything that needs to be improved or changed. I'm excited to hear your thoughts and continue working on this feature.

I made the following changes:

• Added GPT_TOGETHERAI_MODELS
• Set default max tokens from Together.AI to 64,000 tokens
• Added description for STREAM=true in .env file
• In openai_helper.pyadded a new function generate_image_flux()
• In telegram_bot.py edited image() function to handle both flux and dall-e based on the .env file
• added FLUX_GEN=false in .env file which has to be true while the provider is TogetherAI

Thanks for maintaining such a great project!