When I run fedpkg update, fedpkg should be able to determine automatically if my build is a "newpackage" update or not.

If my build's package has no other builds in the Koji -candidate tag (eg "epel8-candidate"), then fedpkg update should pre-fill the type= option as type=newpackage.

Steps to reproduce:
1. Request a new epel8 branch for a package.
2. Switch to the epel8 branch (git fetch && fedpkg switch-branch epel8).
3. Push everything that I need to the epel8 branch.
4. Build the package (fedpkg build)
5. Create the bodhi update (fedpkg update)
6. Look at the bodhi.template file that fedpkg has opened in my $EDITOR

Actual results:
fedpkg's bodhi.template file is asking me to fill out the type= of this update.

Expected results
fedpkg should query Koji to see that there are no other builds in this build's -candidate tag, and simply prepopulate type= as type=newpackage.

This will make it easier for packagers to get new packages into Fedora and EPEL. It will also be very easy for a packager to override fedpkg's default value if we guess the wrong value in some corner case.