feature: support OpenAI compatible APIs in aws-genai plugin

[vmahe35]

🔖 Feature description

I suggest to add a new langgraph.openai.baseUrl parameter in the settings of the aws-genai plugin, that would look like this:

genai:
  agents:
    general: # This matches the URL in the frontend
      description: ...
      prompt: ...
      langgraph:
        openai:
          baseUrl: ${OPENAI_API_BASE_URL}
          apiKey: ${OPENAI_API_KEY}
          modelName: ${QUERY_MODEL_NAME}

🎤 Context

OpenAI APIs have become a de-facto standard for many AI frameworks and many people today also use Ollama to facilitate the management of models as a Service.
Ollama provides its own API but also has an OpenAI compatible interface.

Therefore, it would make sense to be able to configure another baseURL parameter for the endpoints than the default OpenAI endpoint (https://api.openai.com/v1).

✌️ Possible Implementation

I will submit a PullRequest for it (already developed and tested on my local dev env).