Tracker for deployment of cargo vendor-filterer

[cgwalters]

I spent a few days writing https://github.com/cgwalters/cargo-vendor-filterer when I noticed how out of control crazy the vendor tarball for rpm-ostree is. It's still crazy of course, just less so.

This issue tracks deployment of it across our repositories.

Existing PRs:

• Use cargo vendor-filterer rpm-ostree#3786
• Configure cargo vendor-filterer coreos-installer#894

Let's use it for those two projects, verify things work before taking it farther.

• PR the Cargo.toml changes to the other Rust repos that produce a vendor tarball
  • afterburn
  • bootupd
  • ssh-key-dir
  • zincati
• update the checklist template to use vendor-filterer everywhere