Update legacy transferwise Snowflake loader config with key pair authentication #2313

Hi!

I am trying to switch our Snowflake service user to key pair authentication in the Transferwise Snowflake loader, but I notice the instructions doesn't mention how to use this authentication method. Could you update the instructions? Basically remove password and add entry for PRIVATE_KEY and note that this path.

For context, Snowflake is phasing our password authentication for service users.

The rendered docs are here and file that powers this seems to be this one. I think this is the repo that explains how to use the underlying connector, but I don't fully understand how it connects to the YAML.

Bonus question. Could we include the YAML setup and is it possible to lock the version of the loader?