driver/db-start-of-week can vary based on session variables or connection options but defmulti only accepts driver

https://github.com/metabase/metabase/blob/master/src/metabase/driver.clj#L810

Start at src/metabase/driver.clj around line 810 and inspect db-start-of-week and its defmulti dispatch. Trace how session variables or connection options can affect the result, then identify the tests and acceptance criteria needed to represent those cases; the issue does not name a test or specify the intended dispatch design.

Written by the indexing model from the issue text.