feat: add audit for unused content fragments

[holtvogt]

This PR introduces a new audit to monitor and identify unused content fragments on AEM to optimize content governance and reduce system overhead.

What's New

Content Fragment Unused Audit (content-fragment-unused): Analyzes content fragments in AEM to identify unused content that has remained in draft, modified, or unpublished states for extended periods (90+ days). The audit categorizes fragments by their lifecycle status and provides detailed statistics including age distribution, counts, and percentages to help teams prioritize cleanup efforts.

The audit identifies four categories of unused content:

• NEW: Fragments created but never published
• DRAFT: Fragments created and modified but never published
• UNPUBLISHED: Fragments that were published then unpublished without further modifications
• MODIFIED: Previously published fragments with unpublished changes

Use Case

Content governance optimization for AEM Sites: Automatically detect stale and unused content fragments across AEM Sites by analyzing content lifecycle status and age. The audit provides actionable insights to help teams identify orphaned drafts, abandoned work-in-progress, and outdated content, enabling focus on active content management. Each finding includes detailed metadata such as fragment age, last modification date, and publication history to support informed cleanup decisions.

Related

Depends on adobe/spacecat-shared#1135

[github-actions]

This PR will trigger a minor release when merged.