[Feature] python: Provide a way get or use the max context size supported by the LLM

[Ben-Epstein]

Feature Request

Currently, the default context is always set to 2048, but many models have a larger context window. I tried to showcase a simple first step by having the context limit as a part of the models3.json, but that was rejected and requested that I open an issue instead.

According to @cebtenzzre ref this is already done in the GUI.

Request: Set the default context length in the bindings to None, and if not set, dynamically set the context length based on the chosen model