add @types/pg and set correct type

Signed-off-by: Joep Peeters <joep.peeters@nedap.com>

packages/backend-common/package.json

@@ -78,6 +78,7 @@
     "morgan": "^1.10.0",
     "node-fetch": "^2.6.7",
     "node-forge": "^1.3.1",
+    "pg": "^8.9.0",
     "raw-body": "^2.4.1",
     "request": "^2.88.2",
     "selfsigned": "^2.0.0",
@@ -110,6 +111,7 @@
     "@types/mock-fs": "^4.13.0",
     "@types/morgan": "^1.9.0",
     "@types/node-forge": "^1.3.0",
+    "@types/pg": "^8.6.6",
     "@types/recursive-readdir": "^2.2.0",
     "@types/stoppable": "^1.1.0",
     "@types/supertest": "^2.0.8",