refactor: support both Anthropic and LiteLLM model class providers

What does this merge request do and why?

This MR adds support for both the ChatAnthropic and ChatLiteLLM model class providers when instantiating an agent instance.

Related discussion: #541 (closed)

How to set up and validate locally

1. To use ChatAnthropic class, update the chat/react.yml config following:

   name: Claude 3 ReAct Chat agent
   model:
     name: claude-3-sonnet-20240229
     params:
       model_class_provider: anthropic
       temperature: 0.0
       timeout: 60
       max_tokens: 2_048
       max_retries: 1
       # Please, check `agents.config.models.ChatAnthropicParams` for the list of supported model parameters

2. To use ChatLiteLLM class, update the chat/react.yml config following:

    model:
     name: claude-3-sonnet-20240229
     params:
       model_class_provider: lite_llm
       temperature: 0.0
       timeout: 60
       max_tokens: 2_048
       max_retries: 1
       # Please, check `agents.config.models.ChatLiteLLMParams` for the list of supported model parameters

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.