GitHub action to add copyright headers

[flanakin]

⚠️ Problem

Copyright headers are required, but easily forgotten.

🛠️ Solution

Create a GitHub action that runs the Add-CopyrightHeaders script for every PR.
If any files are updated, commit and push to the branch.
If any new file types are discovered, block the PR and leave a comment to add the comment characters or exclude the file type.
Re-run the check with each commit.

ℹ️ Additional context

Details about updating the script are documented at src/scripts/README.md.

🙋‍♀️ Ask for the community

We could use your help:

1. Please vote this issue up (👍) to prioritize it.
2. Leave comments to help us solidify the vision.