Update prometheus requirement from 0.13 to 0.14 in /reference-apps/rust (#12)

Updates the requirements on [prometheus](https://github.com/tikv/rust-prometheus) to permit the latest version.
- [Changelog](https://github.com/tikv/rust-prometheus/blob/master/CHANGELOG.md)
- [Commits](tikv/rust-prometheus@v0.13.0...v0.14.0)

---
updated-dependencies:
- dependency-name: prometheus
  dependency-version: 0.14.0
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

reference-apps/rust/Cargo.toml

@@ -18,5 +18,5 @@ mysql_async = "0.36"
 mongodb = "3.1"
 redis = { version = "0.27", features = ["tokio-comp", "cluster-async"] }
 lapin = "3.7"
-prometheus = "0.13"
+prometheus = "0.14"
 lazy_static = "1.4"