Create build infrastructure for running tests with oldest, newest and future version of database and driver.

[schauder]

Currently we only run our tests with a single database/driver version combination per supported database.

We should improve that to run tests with

• the oldest driver/database version combination we support. This will mostly be a form of documentation of the supported versions
• the current/newest versions. This is what we already have
• If available, i.e. for the open source databases we should also run with snapshots of upcoming versions

These builds should run at maximum once a day, maybe even just once a week.