release-22.2: sql: disallow using cluster_logical_timestamp as column default when backfilling

[Xiang-Gu]

Backport 1/1 commits from #98696.

/cc @cockroachdb/release

---

Previously, ADD COLUMN ... DEFAULT cluster_logical_timestamp() would crash the node and leave the table in a corrupt state. The root cause is a nil pointer dereference. This commit fixed it by returning an unimplemented error and hence disallow using this builtin function as default value when backfilling.

Fixes: #98269
Release note (bug fix): fixed a bug as detailed in #98269.
Release justification: fixed a bug that caused node crash.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is