optimize startup sequence performance (#19009)

- bucket metadata does not need to look for legacy things
  anymore if b.Created is non-zero

- stagger bucket metadata loads across lots of nodes to
  avoid the current thundering herd problem.

- Remove deadlines for RenameData, RenameFile - these
  calls should not ever be timed out and should wait
  until completion or wait for client timeout. Do not
  choose timeouts for applications during the WRITE phase.

- increase R/W buffer size, increase maxMergeMessages to 30

cmd/erasure-server-pool.go

@@ -1958,11 +1958,7 @@ func (z *erasureServerPools) HealFormat(ctx context.Context, dryRun bool) (madmi
 }
 
 func (z *erasureServerPools) HealBucket(ctx context.Context, bucket string, opts madmin.HealOpts) (madmin.HealResultItem, error) {
-	// Attempt heal on the bucket metadata, ignore any failures
-	hopts := opts
-	hopts.Recreate = false
-	defer z.HealObject(ctx, minioMetaBucket, pathJoin(bucketMetaPrefix, bucket, bucketMetadataFile), "", hopts)
-
+	// .metadata.bin healing is not needed here, it is automatically healed via read() call.
 	return z.s3Peer.HealBucket(ctx, bucket, opts)
 }