feat: Single drive XL implementation (#14970)

Main motivation is move towards a common backend format
for all different types of modes in MinIO, allowing for
a simpler code and predictable behavior across all features.

This PR also brings features such as versioning, replication,
transitioning to single drive setups.

cmd/server-main_test.go

@@ -27,7 +27,7 @@ import (
 func TestNewObjectLayer(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
-	// Tests for FS object layer.
+	// Tests for ErasureSD object layer.
 	nDisks := 1
 	disks, err := getRandomDisks(nDisks)
 	if err != nil {
@@ -39,7 +39,7 @@ func TestNewObjectLayer(t *testing.T) {
 	if err != nil {
 		t.Fatal("Unexpected object layer initialization error", err)
 	}
-	_, ok := obj.(*FSObjects)
+	_, ok := obj.(*erasureSingle)
 	if !ok {
 		t.Fatal("Unexpected object layer detected", reflect.TypeOf(obj))
 	}