Add support for Snowflake via JDBC

Nobody has claimed this yet.

I used Postico every day when the company I was working for back then was using Amazon Redshift. When we transitioned to Snowflake, I had to replace Postico with Snowflake's web-based query editor which works well but lacks some of features of a native macOS app.

Nearly all of the projects I'm involved in and everyone I know is using Snowflake or is in the process of transitioning. I was wondering how much effort it would be to add JDBC support and change parts of the connection modal so that Postico supports Snowflake.

I understand you've built a prototype for JDBC-based connection strings in #377 ([link to post](https://github.com/jakob/Postico/issues/377#issuecomment-442546194)) so I'm hoping Postico maybe already uses JDBC under the hood.

BTW I'm not expecting full support for the Snowflake SQL dialect. If I could use Postico to connect to Snowflake databases and run queries, read-only if need be, I'd be a happy man.

Let me know if I can support in any way e.g. by providing more information or contributing code or resources. I've never developed a macOS app but I do have a software engineering background so I could roll up my sleeves.

Start by reading the JDBC-based connection-string prototype discussed in issue #377 and reviewing the connection modal mentioned here. Define the scope needed for Snowflake connections and query execution, with read-only access as an acceptable outcome; the issue is complete when Postico can connect to Snowflake and run queries.

Written by the indexing model from the issue text.