GitHub Issues Workflow for Chef

This RFC codifies the workflow of Chef maintainers while maintaining issues and contributions for Chef.

Special thanks to @btm / @lamont-granquist / @danielsdeleo / @mcquin / @adamedx / @jdmundrawala  who has helped put the first version come together.
I added an "Incomplete Contribution" tag that I've applied to some PRs+Issues that we've closed after they appeared to be abandoned.  Trying to both make those issues searchable and to attempt to indicate that we didn't decide to not do it or not-a-bug it, but just that the resources were lacking to rescue it.