fix: backend/package.json & backend/package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-PATHTOREGEXP-8482416
- https://snyk.io/vuln/SNYK-JS-BODYPARSER-7926860
- https://snyk.io/vuln/SNYK-JS-EXPRESS-7926867
- https://snyk.io/vuln/SNYK-JS-SEND-7926862
- https://snyk.io/vuln/SNYK-JS-SERVESTATIC-7926865
- https://snyk.io/vuln/SNYK-JS-PATHTOREGEXP-7925106
- https://snyk.io/vuln/SNYK-JS-COOKIE-8163060

Author: snyk-io[bot]