I was looking at the help text for request-branch and completely
overlooked the instruction to have a look at request-repo. To imporve
this, I used a couple of strings and cloned the text into all affected
commands.

Also fixed some explicit fedpkg mentions with string interpolation in
the parts I touched.

I ran make test and tests passed except for some Python versions where building wheels of dependencies failed.

I also did an editable install and ran the affected commands with --help. The output for request-repo is unchanged and request-test-repo and request-branch work as expected.