Bump moment from 2.20.1 to 2.29.4 in /backend

Bumps [moment](https://github.com/moment/moment) from 2.20.1 to 2.29.4.
- [Release notes](https://github.com/moment/moment/releases)
- [Changelog](https://github.com/moment/moment/blob/develop/CHANGELOG.md)
- [Commits](moment/moment@2.20.1...2.29.4)

---
updated-dependencies:
- dependency-name: moment
  dependency-type: direct:production
...

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