Support custom email alias for GH accounts

[Naros]

@ebullient as requested:

Some folks have GitHub usernames that align with professional naming conventions (e.g. first initial + last name), similar to our corporate email addresses. However, others, including myself, created GitHub accounts many years ago with an alias handle that is not immediately recognizable to colleagues or external collaborators and sponsors.

When corresponding about foundation-related matters with external folk, such as sponsors, my current handle isn't as clear as it could be. Having an alias like ccranfor@[domain] or chris.cranford@[domain] would certainly be helpful in these circumstances.

So could we implement an additional mailbox alias that forwards incoming mail from my decorative alias to my GH account email?