This configures the nightly build to generate release notes and provides
a template for organizing them. The organization is done through
labeling of PRs and categorizing them based on those labels. I've tried
to provide a rough categorization that seems reasonable for folks.
While doing this I looked at our PR labeling and found a few bugs that
were preventing many labels form being attached. I've fixed those and
significantly expanded the coverage of file-based labeling. I've also
added code to do author-based labeling for automated PRs so those can be
separated out from human PRs.
