Use copy-pr-bot

[ajschmidt8]

This PR replaces the copy_prs functionality from the ops-bot with the new dedicated copy-pr-bot GitHub application.

Thorough documentation for the new copy-pr-bot application can be viewed below.

• https://docs.gha-runners.nvidia.com/apps/copy-pr-bot/

Important: copy-pr-bot enforces signed commits. If an organization member opens a PR that contains unsigned commits, it will be deemed untrusted and therefore require an /ok to test comment. See the GitHub docs here for information on how to set up commit signing.

Any time a PR is deemed untrusted, it will receive a comment that looks like this: rapidsai/ci-imgs#63 (comment).

Every subsequent commit on an untrusted PR will require an additional /ok to test comment.

Any existing PRs that have unsigned commits after this change is merged will require an /ok to test comment for each subsequent commit or the PR can be rebased to include signed commits as mentioned in the docs below:
https://docs.gha-runners.nvidia.com/cpr/contributors.

This information is all included on the documentation page linked above.

I've skipped CI on this PR since it's not a change that is tested.