message: use backstage version in backend plugin scaffold
diff: "clean": "backstage-cli clean"
  },
  "dependencies": {
  - "@backstage/backend-common": "^{{version}}",
  - "@backstage/config": "^{{version}}",
  + "@backstage/backend-common": "^{{backstageVersion}}",
  + "@backstage/config": "^{{backstageVersion}}",
  "@types/express": "^4.17.6",
  "express": "^4.17.1",
  "express-promise-router": "^3.0.3",
  "yn": "^4.0.0"
  },
  "devDependencies": {
  - "@backstage/cli": "^{{version}}",
  + "@backstage/cli": "^{{backstageVersion}}",
  "@types/supertest": "^2.0.8",
  "supertest": "^4.0.2",
  "msw": "^0.20.5"
  