Label pull requests automatically from changed paths and title prefix #5761

What is the problem the feature request solves?

Pull requests are labeled by hand. Open pull requests mostly carry a type label (enhancement, bug, performance, test, build) and one or two area:* labels, but most merged pull requests carry no label at all, so the labels are not a reliable view of what changed where, and every label costs a maintainer a click.

Describe the potential solution

A labeler workflow that adds area:* labels from the paths a pull request touches and the type label from its conventional commit prefix, mirroring the scheme maintainers apply by hand. Labels are only added, never removed, so hand edits stay, and the gating labels that trigger extra test runs (run-spark-*-tests, run-iceberg-tests, skip-ci) are never touched. Path rules checked against the open pull requests that carry area labels today.

Additional context

Issues already get requires-triage automatically through label_new_issues.yml; this extends the same idea to pull requests.