release-21.1: sql: unsafe_upsert_descriptor to bump descriptor ID sequence

[ajwerner]

Backport 1/1 commits from #68662.

/cc @cockroachdb/release

---

Previously, it was possible to use this descriptor repair function to
insert a new descriptor with an ID greater than any descriptor in the
cluster and would not update the descriptor ID sequence value.
Subsequent CREATE statements would therefore write descriptors
with IDs smaller or equal to the descriptor inserted previously. In the
equal case, this corrupts the schema.

This commit adds a test that checks that the ID is less than the value
stored in the descriptor ID sequence. When that is not the case:

• an error is returned when the force flag is not set,
• otherwise, the sequence value is incremented appropriately.

Fixes #68230.

Release note: None

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues.
• 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 

[rafiss]

this is stale