[Feature]: Support for Github Models (Github Marketplace)

Description

Currently opencommit doesn't support Github Models API calls. It would be nice to have the support for Github models, as they're free to use (if you get your access granted) and gives you free API key to request differents models, GPT 4o included

Suggested Solution

The user could provide a GITHUB_TOKEN (free) instead of the OpenAI (not free) API key for the LLM requests.

Usage :

import os
from openai import OpenAI

token = os.environ["GITHUB_TOKEN"]
endpoint = "https://models.inference.ai.azure.com"
model_name = "gpt-4o-mini"

client = OpenAI(
    base_url=endpoint,
    api_key=token,
)

response = client.chat.completions.create(
    messages=[
        {
            "role": "system",
            "content": "You are in charge to create a commit name for all those differences:",
        },
        {
            "role": "user",
            "content": "What is the capital of France?",
        }
    ],
    model=model_name,
    temperature=1.,
    max_tokens=1000,
    top_p=1.
)

print(response.choices[0].message.content)

Alternatives

No response

Additional Context

No response

Start by tracing how opencommit currently configures OpenAI and other LLM providers, then compare those requests with the GitHub Models example in the issue. Define how GITHUB_TOKEN, the models.inference.ai.azure.com endpoint, and model selection should be exposed. Done means GitHub Models requests work without an OpenAI API key and are covered by appropriate tests.