Detect PRs with exessively large files

[mattclay]

Detect PRs with excessively large files (size TBD). If any are found, comment on the PR and add the needs_revision label. This will prevent accidentally merging PRs with oversized content which will then permanently bloat the repo.

[mattclay]

Example: ansible/ansible#58059

https://github.com/ansible/ansible/blob/39b5ed56a09be1ffdc5b6d081fb1724bc095c6f3/test/integration/targets/s3_bucket_notification/files/function.zip is 40.7 MB