Key-pair authentication for Snowflake

[radeusgd]

Apart from the OAuth flow (#12011) we also want users to rely on key-pair authentication when connecting to Snowflake.

• Allow Snowflake connection to take a private key file from disk to use when connecting.
• Allow Snowflake connection to take an Enso_Secret that contains the private key.
• Create a helper method that generates the key-pair and stores the private key as an Enso_Secret and the public key as an Enso_File next to it.
  • It should have instructions how to set up the public key in Snowflake: https://docs.snowflake.com/en/user-guide/key-pair-auth#assign-the-public-key-to-a-snowflake-user