Add a helper method to convert an RDMResponse to a NACKing RDMResponse

[peternewman]

(cherry picked from commit 324b4ec)

[peternewman]

Ping @kripton in case you missed it...

[kripton]

Looks all good, new test case PASSes on my machine and FAILs if I modify it (just to make sure it was actually run)

[kripton]

@peternewman: Interesting, even though the branch is in your repo, I was able to rebase it on top of latest master using GitHub's web interface. I'll merge it as soon as all CI checks are green.

[peternewman]

@peternewman: Interesting, even though the branch is in your repo, I was able to rebase it on top of latest master using GitHub's web interface.

That may be because of this:
https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork

Or possibly simply because you've got OLA write access, but I suspect not unless that box was ticked from the description...