fix(deps): bump @nestjs/config from 1.2.1 to 3.1.1 in /backend

Bumps [@nestjs/config](https://github.com/nestjs/config) from 1.2.1 to 3.1.1.
- [Release notes](https://github.com/nestjs/config/releases)
- [Changelog](https://github.com/nestjs/config/blob/master/.release-it.json)
- [Commits](nestjs/config@1.2.1...3.1.1)

---
updated-dependencies:
- dependency-name: "@nestjs/config"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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