Fix broken prom.lib link in console docs

[cnaples79]

Summary

• replace the dead prom.lib link with a reference to the console_libraries examples shipped in Prometheus release artifacts

Rationale

• prom.lib was removed upstream, so the existing link 404s; this keeps the guidance without pointing to a missing file.

Testing

• not run (docs-only change)

Fixes #2649

[jan--f]

Hey @cnaples79, #2812 recently added a warning to the docs referring back the the 2.x code stream. Given that we no longer include the examples in the release payload, perhaps this change here is no longer needed?