Avoid ListBuckets() call instead rely on simple HTTP GET (#8475)

This is to avoid making calls to backend and requiring
gateways to allow permissions for ListBuckets() operation
just for Liveness checks, we can avoid this and make
our liveness checks to be more performant.

cmd/gateway/s3/gateway-s3.go

@@ -261,7 +261,11 @@ func (g *S3) NewGatewayLayer(creds auth.Credentials) (minio.ObjectLayer, error)
 
 	s := s3Objects{
 		Client: clnt,
+		HTTPClient: &http.Client{
+			Transport: minio.NewCustomHTTPTransport(),
+		},
 	}
+
 	// Enables single encryption of KMS is configured.
 	if minio.GlobalKMS != nil {
 		encS := s3EncObjects{s}
@@ -283,7 +287,8 @@ func (g *S3) Production() bool {
 // s3Objects implements gateway for MinIO and S3 compatible object storage servers.
 type s3Objects struct {
 	minio.GatewayUnsupported
-	Client *miniogo.Core
+	Client     *miniogo.Core
+	HTTPClient *http.Client
 }
 
 // Shutdown saves any gateway metadata to disk
@@ -294,6 +299,8 @@ func (l *s3Objects) Shutdown(ctx context.Context) error {
 
 // StorageInfo is not relevant to S3 backend.
 func (l *s3Objects) StorageInfo(ctx context.Context) (si minio.StorageInfo) {
+	si.Backend.Type = minio.BackendGateway
+	si.Backend.GatewayOnline = minio.IsBackendOnline(ctx, l.HTTPClient, l.Client.EndpointURL().String())
 	return si
 }