Extend validate-metadata.yml trigger paths to include opt-out-plugins.json and/or reports/

[Maanvi212006]

Proposal

The current validate-metadata.yml only triggers validation when files under **/modernization-metadata/** are changed.

I propose extending the paths trigger to also cover:

• opt-out-plugins.json (at root level) — because this file directly affects which plugins receive (or skip) automatic modernization PRs. Changes here should be validated.

For the reports/ folder I'm unsure:

• Pros: Reports like aggregated_migrations.json, failed migrations, and recipe summaries are important for downstream projects (e.g. GSoC Plugin Modernizer Stats Visualization).
• Cons: They are derived/aggregated data generated by other workflows, so validating them might be somewhat redundant.

Questions:

• Should we add opt-out-plugins.json to the trigger paths?
• Should we also include reports/** (or only specific files)?
• Or keep validation strictly limited to raw modernization metadata?