release-22.2: sql/schmachanger: use more friendly language for fallback

[blathers-crl]

Backport 1/1 commits from #98112 on behalf of @fqazi.

/cc @cockroachdb/release

---

Previously, the declarative schema changer used slightly
alarming language when falling back. To address this,
this patch removes the word failure and uses softer
language. Also, the logging level is reduced to remove
this message by default.

Fixes: #97922

Release note (bug fix): Previously the declarative schema changer would emit alarming
messages of the form: "failed building declarative schema change targets for". These
were non-severe in nature and now disabled by default.

---

Release justification: low risk disabling excessive logging.

[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?

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[ajwerner]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @chengxiong-ruan and @fqazi)

[ajwerner]

I could see a release note if you felt like it.

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @chengxiong-ruan and @fqazi)

[fqazi]

I could see a release note if you felt like it.

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @chengxiong-ruan and @fqazi)

Yes, let me add a release note for this one