Fedora 35 support was dropped, so we can update to a newer Go.
Stable RHEL 8 and 9 and Fedora 36 ships Go 1.18, so let's switch to it.
"//go:build" directives are now apparently enforced by go fmt, so that's why
there were added.
Also, all the github actions were adjusted to use Go 1.18.
Signed-off-by: Ondřej Budai <ondrej@budai.cz>
Add a new generic container registry client via a new `container`
package. Use this to create a command line utility as well as a
new upload target for container registries.
The code uses the github.com/containers/* project and packages to
interact with container registires that is also used by skopeo,
podman et al. One if the dependencies is `proglottis/gpgme` that
is using cgo to bind libgpgme, so we have to add the corresponding
devel package to the BuildRequires as well as installing it on CI.
Checks will follow later via an integration test.
