Bump mongodb and mongoose in /backend

Bumps [mongodb](https://github.com/mongodb/node-mongodb-native) to 4.17.1 and updates ancestor dependency [mongoose](https://github.com/Automattic/mongoose). These dependencies need to be updated together.


Updates `mongodb` from 4.16.0 to 4.17.1
- [Release notes](https://github.com/mongodb/node-mongodb-native/releases)
- [Changelog](https://github.com/mongodb/node-mongodb-native/blob/v4.17.1/HISTORY.md)
- [Commits](mongodb/node-mongodb-native@v4.16.0...v4.17.1)

Updates `mongoose` from 6.11.3 to 6.12.0
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/master/CHANGELOG.md)
- [Commits](Automattic/mongoose@6.11.3...6.12.0)

---
updated-dependencies:
- dependency-name: mongodb
  dependency-type: indirect
- dependency-name: mongoose
  dependency-type: direct:production
...

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