Offer SQL-Only Mode for JDBC supported databases

This is almost certainly a bad idea, but opening an issue to provide a place to discuss/debate.

What if we offered a "raw-mode-only" level of database support for anything JDBC supports? We'd only offer native query access, and no other Metabase Magic.

Pros:
- Expand the list of available databases
- Allow us to defer actually writing + testing a real driver until there's direct evidence of people using MB + that DB together

Cons:
- Crippled experience for these databases
- UX complexity?

This issue is a proposal for raw SQL-only support for databases accessible through JDBC, but it names no files, entry points, or tests. First review how Metabase currently supports JDBC databases and native queries. Done would require a decided scope for supported databases, user experience, and testing, which the discussion has not established.

Written by the indexing model from the issue text.