feat: support model in request about edgen HOT 2 CLOSED

There is an ambiguity with the approach: if the model is in a subdirectory, e.g.:
~/.local/share/edgen/models/chat/completions/my-models/top-models/my-top-model.gguf
It could be a file or a model identifier with "my-models" as owner, "top-models" as repo and "my-top-model.gguf" as model. If the file exists, the huggingface API will be by-passed. Otherwise, edgen will try to download it from huggingface.

from edgen.

The model parameter in ai endpoint requests is now considered again. There are four valid cases:

• model contains a path model-file, such that the <config model dir> + "/" + <model-file> exists, e.g.:
  "model": "my-model.gguf" => ~/.local/share/edgen/models/chat/completions/my-model.gguf
  In this case, the huggingface API is bypassed. If the file does not exist, the endpoint returns "No Such Model".
• model contains a model in the format: owner/repo/model, e.g.:
  "TheBloke/TinyLlama-1.1B-Chat-v1.0-GGUF/tinyllama-1.1b-chat-v1.0.Q2_K.gguf" =>
  ~/.local/share/edgen/models/chat/completions/models--TheBloke--TinyLlama-1.1B-Chat-v1.0-GGUF
  In this case, the huggingface API is used to identify the model and, if necessary, to download the model.
• model contains "default" (case-insensitive): model as defined in the config is used. Whether the the huggingface API is used or not depends on what is configured there (a manually managed file or a huggingface-managed model).
• model contains nothing (e.g. "", " ", " ", etc.): like "default".

from edgen.