[Feature request]: Offer an API with configurable arguments

It would be nice to have a lua API exposed to the user which could be called with various arguments, such as the model type. This would allow for greater control and interoperability with other plugins. as well as opening the door for more flexibility if other LLMs are introduced.

For my particular use case, I am using a [telescope extension](https://github.com/HPRIOR/telescope-gpt/tree/main) which provides a picker over various chat gpt functions, such as chat and interactive modes. I would like to be able to declare options in the extension, like: `chat-cheap`, or `chat-expensive` that offer an easy way to switch between gpt3 and gpt4 models.

Another useful feature of the proposed API would be the ability to specify visual selections.

Ideally this would be available for most the functionality provided by the plugin: ChatGPT, ChatGPTEditWithInstruction, ChatGPTRun

Start by tracing the existing ChatGPT, ChatGPTEditWithInstruction, and ChatGPTRun entry points, then review the linked telescope extension for the requested calling patterns. Define the API surface for configurable model arguments and visual selections, and verify that these functions support the proposed options across the plugin's functionality.

Written by the indexing model from the issue text.