pip(deps): bump prometheus-client from 0.12.0 to 0.18.0

Bumps [prometheus-client](https://github.com/prometheus/client_python) from 0.12.0 to 0.18.0.
- [Release notes](https://github.com/prometheus/client_python/releases)
- [Commits](prometheus/client_python@v0.12.0...v0.18.0)

---
updated-dependencies:
- dependency-name: prometheus-client
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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