local LLM -- option to select *.gguf models by myself

Hello.

I am happy with this extension. It is the only one, that works without any dependencies and therefore it is instantly usable within VScode. Thank you for bringing us such an extension. I have **some requests**:

It would be nice, if we could have a option to select the *.gguf model file by our own. I can download it somewhere (f.e. huggingFace) and inside the options of FireCoder i can select the file. I recognized that the models are saved inside C:\ drive. inside the USERS subfolder: ".firecoder". If its possible it would also be very handy, if we could have an option where to store downloaded models.

In my case, the drive C: is reserved for the OS and stays clean. I put heavy stuff onto the D: partition. (Windows OS). I managed to use the MkLink command, to alias this folder to drive D:.

No files, tests, or entry points are named. Start by locating the VS Code settings and the existing model download/storage flow, then determine how user-selected .gguf files and a configurable model directory should fit together; done means both requested options work without breaking the current model behavior.

索引モデルが issue の本文から書いたものです。