sql: add query cache collision testing

We currently have limited testing for the case when the same SQL is run concurrently by different users / on different databases against the same query cache. More testing for this case could have caught https://github.com/cockroachdb/cockroach/issues/102375. Our logic tests already allow switching the user and db session with the `user` directive. We should add some tests that repeatedly run the same SQL on similar schemas from different users to verify that the query cache is correctly invalidated in the case when it is thrashing. We may also want to add support for similar testing in our randomized tests.

Jira issue: CRDB-28320