Bump json-bigint and firebase-admin in /backend

Bumps [json-bigint](https://github.com/sidorares/json-bigint) to 1.0.0 and updates ancestor dependency [firebase-admin](https://github.com/firebase/firebase-admin-node). These dependencies need to be updated together.


Updates `json-bigint` from 0.3.1 to 1.0.0
- [Release notes](https://github.com/sidorares/json-bigint/releases)
- [Commits](sidorares/json-bigint@v0.3.1...v1.0.0)

Updates `firebase-admin` from 8.13.0 to 11.0.1
- [Release notes](https://github.com/firebase/firebase-admin-node/releases)
- [Commits](firebase/firebase-admin-node@v8.13.0...v11.0.1)

---
updated-dependencies:
- dependency-name: json-bigint
  dependency-type: indirect
- dependency-name: firebase-admin
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]