Adding Snowflake Provider Support + Distribution Template

[sfc-gh-alherrera]

Adds support for inference with Snowflake's Cortex endpoint. See docs for more background on Cortex:https://docs.snowflake.com/en/user-guide/snowflake-cortex/cortex-llm-rest-api

Testing

• built a new stack from scratch using remote::snowflake for the Inference API
• ran python -m llama_stack.apis.inference.client localhost
• directly submitted request to the llama stack server