chore(deps): bump on-headers and ln-service in /backup-server

Removes [on-headers](https://github.com/jshttp/on-headers). It's no longer used after updating ancestor dependency [ln-service](https://github.com/alexbosworth/ln-service). These dependencies need to be updated together.


Removes `on-headers`

Updates `ln-service` from 56.13.0 to 57.27.0
- [Changelog](https://github.com/alexbosworth/ln-service/blob/master/CHANGELOG.md)
- [Commits](https://github.com/alexbosworth/ln-service/commits)

---
updated-dependencies:
- dependency-name: on-headers
  dependency-version: 
  dependency-type: indirect
- dependency-name: ln-service
  dependency-version: 57.27.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]