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/metacache-manager.go

@@ -56,7 +56,7 @@ func (m *metacacheManager) initManager() {
 			objAPI = newObjectLayerFn()
 		}
 
-		if !globalIsErasure {
+		if globalIsGateway {
 			return
 		}