Follow up on OSI ai_context and custom_extensions mapping in snowflake yaml

As discussed in the initial [PR](https://github.com/open-semantic-interchange/OSI/pull/98) for OSI->Snowflake YAML converter, there are some concepts in the OSI ai_context and custom_extensions that do not have a direct mapping in Snowflake YAML (e.g., field-level instruction and examples, ai_context on relationships, etc.). We should follow up with the Snowflake team on how we should add support and properly convert these in Snowflake YAML so that there is no metadata loss.