Fix env sample

[hnishi]

Summary by CodeRabbit

• New Feature: Introduced the MODEL_NAME environment variable to allow users to specify the model they want to use. Currently supports "gpt-4" and "gpt-3.5-turbo".
• New Feature: Added an optional OPENAI_ORGANIZATION environment variable for users who are part of an OpenAI organization.
• Refactor: Removed hardcoded values for MODEL_NAME and MODEL_MAX_TOKEN_LENGTH in configuration.py, improving flexibility and maintainability.
• Documentation: Updated README.md and .env.sample to reflect the new environment variables and their usage.

[github-actions[bot]]

CodeRabbit

Walkthrough

The changes primarily focus on enhancing the configuration of the application by introducing environment variables for model selection and organization. The MODEL_NAME and OPENAI_ORGANIZATION are now configurable, with the former influencing the MODEL_MAX_TOKEN_LENGTH. The README and sample environment files have been updated to reflect these changes.

Changes

File(s)	Summary
.env.sample, README.md	Removed export keyword from environment variable assignments in shell script. Added new environment variables MODEL_NAME and OPENAI_ORGANIZATION. Updated README to reflect these changes.
configuration.py	Introduced dynamic setting of MODEL_NAME and MODEL_MAX_TOKEN_LENGTH based on environment variables. An error is raised if an unknown model name is provided.

🐰 "In the land of code, where logic intertwines,

Changes come forth, as bright as sunshine.

With models named and tokens counted,

Our app's flexibility has just been mounted!

So hop along, let's celebrate this day,

For our code just got a better way!" 🎉

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