Refactor users creating separate classes, service and repository

tests/resources/mock_users.json

@@ -0,0 +1,13 @@
+{
+  "12345": {
+    "id": "12345",
+    "username": "Pippo",
+    "fullname": "Pippo Franco",
+    "role": "admin",
+    "credentials": {
+      "username": "pippo.franco",
+      "password": "pippo12345"
+    },
+    "status": 1
+  }
+}