refactor: create storage interface, refactor local, s3, ftp and ssh storage

pkg/storage/storage.go

@@ -0,0 +1,14 @@
+package storage
+
+type Storage interface {
+	Copy(fileName string) error
+	CopyFrom(fileName string) error
+	Prune(retentionDays int) error
+	Name() string
+}
+type Backend struct {
+	//Local Path
+	LocalPath string
+	//Remote path or Destination path
+	RemotePath string
+}