Authorization

[sfc-gh-mkeller]

We don't want snowcli plugins to have to keep implementing their own authorization with Snowflake, so it is going to be central to the core of the CLI.
This needs designing and authorization needs to be copied from the Python connector.

[sfc-gh-mkeller]

After reviewing the current plugin implementation I don't think that it's worth separating out the Python connector from snowcli. Most of them check whether we have been authenticated.
We'll just declare dependency on snowflake-connector-python for now.