[Feature] Use local LLM model

[Dynnammo]

Context

As an open-source advocate, I would like to demonstrate Coverlettergpt using alternative LLMs models provided as instance on HuggingFace.co

Solution

Add the possibility to switch from the Open AI model to a model stored locally

[vincanger]

cool. I'd like to see how this works as well. I cannot guarantee I will deploy the feature to the live app, but if it works well we can at least add it to the repo here!