[llvm] Add github workflow that checks if a private email address was used to contribute to the repo and warn in this case (PR #80514)

[David Spickett via llvm-commits]

DavidSpickett wrote:

> Also I wonder if we should link or include some expanded info why we request people to change this setting and what it does for us. It's not clear for anyone who haven't been part of the conversations why we want it to be public.

Definitely.

If I'm a drive by contributor, I would be more likely to expose my email address if I see there's legitimate reason to do so. If I had other reasons to remain anonymous, I may choose to abandon the PR, but at least I had all the information I need to make that decision (and hopefully not be resentful to llvm as a result).

https://github.com/llvm/llvm-project/pull/80514