Create thirty-flies-flow.md

Author: Feiyang1

.changeset/thirty-flies-flow.md

@@ -0,0 +1,7 @@
+---
+"@firebase/database-types": patch
+"@firebase/database": patch
+---
+
+Added interface `Database` which is implemented by `FirebaseDatabase` to allow the use of interface instead of class for the instance type.
+It solves an issue admin SDK encountered where they only want to export the type, but Typescript thinks they are exporting the actual class.