backupccl: set kv.bulkio.write_metadata_sst.enabled to default false

This patch sets write_metadata_sst cluster setting to false in prep for the
22.2 branch cut, as there's additional work required before this feature gets
used in production. Unit tests may continue to write the MetadataSST because of
a new MetamorphicTestBool.

Setting this to false will also stop the roachtest in #86289 from consistently
failing due to #86806.

Fixes #86289

Release note: none

Release justification: prevents using an experimental feature by default

pkg/ccl/backupccl/backupinfo/BUILD.bazel

@@ -33,6 +33,7 @@ go_library(
         "//pkg/sql/sem/tree",
         "//pkg/sql/stats",
         "//pkg/storage",
+        "//pkg/util",
         "//pkg/util/ctxgroup",
         "//pkg/util/encoding",
         "//pkg/util/hlc",

pkg/ccl/backupccl/backupinfo/manifest_handling.go

@@ -39,6 +39,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
 	"github.com/cockroachdb/cockroach/pkg/sql/stats"
+	"github.com/cockroachdb/cockroach/pkg/util"
 	"github.com/cockroachdb/cockroach/pkg/util/ctxgroup"
 	"github.com/cockroachdb/cockroach/pkg/util/encoding"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
@@ -82,13 +83,11 @@ const (
 
 // WriteMetadataSST controls if we write the experimental new format BACKUP
 // metadata file.
-// kv.bulkio.rite_metadata_sst.enabled set to false by default due to
-// https://github.com/cockroachdb/cockroach/issues/85564.
 var WriteMetadataSST = settings.RegisterBoolSetting(
 	settings.TenantWritable,
 	"kv.bulkio.write_metadata_sst.enabled",
 	"write experimental new format BACKUP metadata file",
-	true,
+	util.ConstantWithMetamorphicTestBool("write-metadata-sst", false),
 )
 
 // IsGZipped detects whether the given bytes represent GZipped data. This check