Implement TogetherAI and Flux Image Generation

[soymh]

Happy New Year to the team!

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.

Thanks for maintaining such a great project!

I made the following changes:

• Added GPT_TOGETHERAI_MODELS in openai_helper.py.
• Added GPT_TOGETHERAI_MODELS to GPT_ALL_MODELS in openai_helper.py
• Set default max tokens from Together.AI to 64,000 tokens in openai_helper.py
• Explained the issue with STREAM=true for TogetherAI
• Implemented generate_image_flux() function in openai_helper.py
• Fixed Flux and Dall-e conflict in telegram_bot.py using the env value FLUX_GEN=false

• Note: I closed the recent PR due to some issues in commits,sorry for that.