Update GPT-4 Turbo pricing and add variant

Related to #3

Adds a new model entry for "gpt-4-turbo-2024-04-09" in the src/data/openai.ts file to reflect the updated pricing structure as per the issue request.

New Model Addition: Introduces the "gpt-4-turbo-2024-04-09" model with an input price of $10 and an output price of $30, aligning with the specified pricing structure.
Existing Pricing Unchanged: Ensures that the pricing for "GPT-4 Turbo", "GPT-4", and "GPT-4-32k" remains as is, since they already match the issue's request.

For more details, open the Copilot Workspace session.

small-tou / llm-price

Update GPT-4 Turbo pricing and add variant #4