release-21.2: kvserver: declare lock spans for AddSSTable

[blathers-crl]

Backport 1/1 commits from #71676 on behalf of @erikgrinaker.

/cc @cockroachdb/release

---

AddSSTable did not declare lock spans, even though it can return
WriteIntentError when encountering unresolved intents (e.g. when
checking for key collisions with DisallowShadowing set). This would
cause the concurrency manager to error with e.g.:

cannot handle WriteIntentError ‹conflicting intents on /Table/84/1/99/49714/0›
for request without lockTableGuard; were lock spans declared for this request?

This patch makes AddSSTable take out lock spans via
DefaultDeclareIsolatedKeys if DisallowShadowing is set. This will
automatically handle any unresolved intents via the concurrency manager.

Release note (bug fix): IMPORT INTO no longer crashes when encountering
unresolved write intents.

---

Release justification: fixes a 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