fix(server): add missing package ajv for validation

Author: Fuss Florian (uid10804)

packages/server/package-lock.json

@@ -33,6 +33,7 @@
   "dependencies": {
     "@types/lowdb": "1.0.9",
     "@types/pino": "6.3.3",
+    "ajv": "^6.12.6",
     "cors": "^2.8.5",
     "express": "^4.17.1",
     "express-graphql": "^0.11.0",