chore: update license headers

[agarvin-nr]

Summary

• Imports the nrlicense tool and uses it to update and add missing license headers
• Changes the third party notice template to refer to NRDOT instead of the infra agent

Validation

• Adds license header checking to CI using nrlicense --check

[agarvin-nr]

At the moment, this checks for the entire repo's license headers in every distribution's CI run. This check doesn't seem to add very much time, but I'm not sure if we'd want to make a separate workflow for this sort of repo-level validation.