Add copyright header year check for new files

[kschiffer]

Summary

This PR adds a new mage target and amends the code-quality workflow file to make sure that all newly introduced files use the copyright header with the correct year.

Changes

• Add mage target mage headers:checkNewFiles
• Improve error logging of header targets so they can appear in the PR diff directly
• Add target to the code quality workflow so that it runs for each new PR

Notes for Reviewers

I'm getting tired of annotating this every other PR. We could even add a target that automatically fixes this, but that would result in an additional commit.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• The steps/process to test this feature are clearly explained including testing for regressions.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.