Add License-File field to package metadata

• I've verified the tests pass with the patch applied in upstream git (on top of the v53.0.0 tag) with tox -e py39 on Fedora 35.
• I've verified the tests pass in %check when built in EPEL 9 mock with a couple of missing packages installed from Fedora 34
• I have verified pyproject-rpm-macros actually add the %license files (via Fedora 34 CI)

How I tested this in mock:

$ mock -r centos-stream+epel-9-x86_64 --init
$ mock -r centos-stream+epel-9-x86_64 --addrepo='http://kojipkgs.fedoraproject.org/repos/f34-build/latest/$basearch/' install python3-jaraco-envs python3-mock python3-pytest-fixture-config python3-pytest-virtualenv
$ mock -r centos-stream+epel-9-x86_64 --dnf-cmd distro-sync  # to downgrade packages that are available in c9s but where installed from Fedora 34
$ mock -r centos-stream+epel-9-x86_64 --no-clean --no-cleanup-after $(centpkg --release c9s srpm | tail -n1 | cut -d' ' -f2) --with tests