Spring AI Refactor Chat Generation Metadata to allow addition of different AI model result/message specific (meta)data.

Currently the ChatGenerationMetadata is not flexible to accommodate the additional (meta)data commit from the various AI models. Currently it is restricted to finishReason and unstructured filters response.

Comment From: markpollack

This has been addressed in the commit https://github.com/tzolov/spring-ai/commit/c308cbc4d21d0e4c2e0f655b28e6a89371778338