Package stub pinger for FCOS

[rfairley]

Since FCOS will want a stub metrics client in the preview release, begin packaging this so it can be built as an RPM pulled into FCOS.

The following are needed to get an RPM pulled into FCOS:

• [x] source release is made of the fedora-coreos-pinger crate (upload to this GitHub page)
• [x] specfile builds rust-fedora-coreos-pinger on Fedora Koji (specfile WIP: https://pagure.io/rust-fedora-coreos-metrics-client). make sure specfile has correct systemd pre,post,preun,postun sections
• [x] package is approved in Fedora
• [x] SCM rpm repo and module are requested and created. add rust-sig group as committer to the rpm package . add tests directory for Koji CI test
• [x] the package is added to the FCOS config (and enable fedora-coreos-pinger service)
• [x] a Koji build of this package is tagged into coreos-pool
• [x] the module build is submitted as a bodhi update for F30
• [x] add module defaults at https://pagure.io/releng/fedora-module-defaults for the pinger
• [x] add exception for the module in coreos-koji-tagger and add to coreos-koji-data

[rfairley]

COPR repo with a built RPM of the MVP: https://copr.fedorainfracloud.org/coprs/rfairley/rust-fedora-coreos-metrics-client/packages/

Koji build: https://koji.fedoraproject.org/koji/taskinfo?taskID=35336277

[rfairley]

Fedora package review request: https://bugzilla.redhat.com/show_bug.cgi?id=1728378

[rfairley]

rust-fedora-coreos-pinger SCM repo was created, also requested a fedora-coreos-pinger module.

Koji build in Rawhide: https://koji.fedoraproject.org/koji/taskinfo?taskID=36329144