Support Custom Model IDs for OpenAI-Compatible Connections

Currently, Agentic Flow AI's OpenAI connection only allows selecting models from a pre-defined list. This makes it impossible to use custom OpenAI-compatible APIs (like Alter) that require specific model IDs (e.g., anthropic#claude-3-5-sonnet-20241022).

To enable wider compatibility and flexibility, please add the ability to:

a) Enter a custom model ID in the OpenAI connection settings, OR b) Add a "Custom Model" field in the agent configuration.

This would allow users to connect to a broader range of LLMs and leverage services like Alter, which provide access to multiple frontier models through a single API key."