build: Include top-level FMF plan into dist tarballs
build: Include top-level FMF plan into dist tarballs

This fixes tmt's `discover: dist-git-source` [1], so that we can
eventually drop the horrible fmf `ref:` hack in packit.yaml.

[1] https://src.fedoraproject.org/rpms/cockpit/pull-request/66

martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit