sql/schmachanger: use more friendly language for fallback

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 defaulta.

Release note: None

pkg/sql/schemachanger/scerrors/errors.go

@@ -75,7 +75,7 @@ func (el EventLogger) HandlePanicAndLogError(ctx context.Context, err *error) {
 			log.InfofDepth(ctx, depth, "done %s in %s", el.msg, redact.Safe(timeutil.Since(el.start)))
 		}
 	case HasNotImplemented(*err):
-		log.InfofDepth(ctx, depth, "failed %s with error: %v", el.msg, *err)
+		log.VEventfDepth(ctx, depth, 1, "declarative schema changer does not support %s: %v", el.msg, *err)
 	case errors.HasAssertionFailure(*err):
 		*err = errors.Wrapf(*err, "%s", el.msg)
 		fallthrough