[chore] Run markdown link check if package.json changes

[niwoerner]

Description

This PR will run the "markdown-link-check" tool if the package.json changes even if no markdown files were updated. This will help to confirm that "markdown-link-check" is still working as expected after a version update/pin.

If 1+ *.md files gets changed AND the package.json gets updated, it will only check the updated files to keep the same behaviour as before.

If only the package.json gets updated it will test all existing *.md files.

Link to tracking issue

Fixes https://github.com/open-telemetry/opentelemetry-collector/issues/11606

Testing

I tested/reproduced this manually:

1. *.md file changes, but package.json not: https://github.com/niwoerner/opentelemetry-collector/actions/runs/11959750938
2. *.md file and package.json changes: https://github.com/niwoerner/opentelemetry-collector/actions/runs/11959777300
3. *.md file doesn't change but package.json: https://github.com/niwoerner/opentelemetry-collector/actions/runs/11959797335

[linux-foundation-easycla[bot]]

• :white_check_mark:login: niwoerner / (11aa90ebb8bf8ad70b64ac4eca6e27caf2d6b172)

The committers listed above are authorized under a signed CLA.

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.63%. Comparing base (6ae9c58) to head (11aa90e). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #11725 +/- ## ======================================= Coverage 91.63% 91.63% ======================================= Files 442 442 Lines 23776 23776 ======================================= Hits 21787 21787 Misses 1618 1618 Partials 371 371 ```

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