Listing chat models for each provider

[SilverMarcs]

Feature Description

List inference models available for any provider

Use Cases

The user may want to see all potential models available for usage by each provider. OpenAI has a /models endpoint for this. Would be nice to have a unified interface of retrieving available endpoints grouped by provider. Currently I only see a long union type of strings hardcoded in the source code but even that is not exported/exposed by the SDK

Additional context

Some providers may not have such a model retrieving endpoint. In such cases, it might suffice to just return the hardcoded union of stings

[jcuenod]

I came looking for this. It's supported by the openai spec with the url https://api.openai.com/v1/models, which covers a lot of implementations. It's also supported by Anthropic but with a different api.