sql: add a test that verifies that the system database schema version is correct after upgrade

[RaduBerinde]

In the 23.2 release cycle, #104714 added a system table but the upgrade does not bump the system database schema version. The PR does change the bootstrap version, so depending on whether we created a cluster on 23.2 or upgraded a cluster from 23.1, we end up with a different schema version.

To prevent this in the future, we should have a test that upgrades a cluster from the previous version and then asserts that the system database schema version is the same as the bootstrap version.

Somewhat related - it's a bit unfortunate that the schema version is an upgrade version (e.g 23.1-32) which will later require special code to determine if this version is acceptable given a minimum supported cluster version of 23.2. It would be ideal if the final schema version matches the latest cluster version. Perhaps the final upgrade step could always be a "finalize schema version" where we bump the version to the bootstrap version.

Jira issue: CRDB-37616

Epic CRDB-37763