[product-manager-impersonator] Label-based quiet mode for automated comments

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Feature Idea

Summary: Add an optional mute-comment-label input so comment-producing workflows skip posting comments (emit noop instead) when a PR/issue is labeled as quiet mode.

Why a Customer Would Want This

Teams running many agent workflows are asking for less comment noise, especially on busy PRs. A label-based quiet mode gives maintainers immediate, reversible control over bot chatter without uninstalling workflows or changing schedules.

Rough Implementation Sketch

• Add an optional mute-comment-label input (default empty/off) to comment-centric workflows.
• In shared comment workflows/prompts, check labels early; if label matches, emit noop with a concise reason instead of add-comment.
• Start with workflows that import shared comment fragments, then roll out to others incrementally.
• Document usage in workflow READMEs and the docs catalog with a one-line example.

Why It Won't Be That Hard

This is mostly input + prompt wiring: shared comment behavior is already centralized via safe-output-add-comment fragments, and noop is already a first-class safe output. The change is additive and backward-compatible (no behavior change unless users opt in).

Evidence

• Comment posting is centralized and widely reused:
  • .github/workflows/gh-aw-fragments/safe-output-add-comment-pr.md:2-8
  • .github/workflows/gh-aw-fragments/safe-output-add-comment-issue.md:2-7
  • rg shows many workflows importing these fragments (e.g., .github/workflows/gh-aw-mention-in-pr.md:18, .github/workflows/gh-aw-pr-review-addresser.md:13, .github/workflows/gh-aw-issue-triage.md:13).
• Project philosophy favors reducing noise and treating noop as success:
  • docs/blog/posts/silence-is-better-than-noise.md:17
  • docs/blog/posts/silence-is-better-than-noise.md:33
• Active customer pain exists now:
  • Combine multiple automated comments into one with collapsable sections #649
  • https://github.com/elastic/integrations/pull/17730 contains multiple comments for the PR Buildkite Detective #647

Not a duplicate of existing PM-impersonator issues (#619, #577, #570, #562, #554, #523, #449, #409, #403, #382), which focus on quick-setup and linting rather than runtime comment-noise controls.

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What is this? | From workflow: Trigger Product Manager Impersonator

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