First, this adds `cargo xtask` following
https://github.com/matklad/cargo-xtask/
We use this to write "external glue scripts" in Rust, not bash.
Specifically we now have e.g. `cargo xtask vendor` which just
wraps running `cargo vendor-filterer`.
Then build on that and add `cargo xtask package-srpm` which generates
a `.src.rpm`.
And build on that by adding the requisite glue to have Fedora's COPR
be able to understand it, so that we can get auto-built and shipped
packages there.
This will make trying out bootc a bit easier.
Signed-off-by: Colin Walters <walters@verbum.org>
