Add support for GitHub hosted models

[siddheshp]

I propose to create a new provider to support GitHub hosted models.

There are some models hosted by GitHub and it would help users of AISuite to use them, in place of paid versions from other providers.

Complete list of models https://github.com/marketplace?type=models

Here is the endpoint URL and model name
endpoint = "https://models.github.ai/inference"
model_name = "openai/gpt-4o-mini"

Users will create "Personal access tokens" on their GitHub account and configure below environment variable which will allow the client object to use these models.
GITHUB_TOKEN=""

Steps to generate PAT https://www.theserverside.com/blog/Coffee-Talk-Java-News-Stories-and-Opinions/How-to-create-a-GitHub-Personal-Access-Token-example