Add support for report-sample

[j-hudecek]

It would be useful to be able to enable 'report-sample' property on any directive. This sends a 40 byte sample of the script or style that broke the directive (see https://csper.io/blog/an-introduction-to-report-uri for more details).

[juunas11]

This looks like it could be useful :) Accepting PRs for this, I don't have time to do this right now.