container: add support for uploading to registries

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.

vendor/github.com/miekg/pkcs11/release.go

@@ -0,0 +1,18 @@
+//go:build release
+// +build release
+
+package pkcs11
+
+import "fmt"
+
+// Release is current version of the pkcs11 library.
+var Release = R{1, 1, 1}
+
+// R holds the version of this library.
+type R struct {
+	Major, Minor, Patch int
+}
+
+func (r R) String() string {
+	return fmt.Sprintf("%d.%d.%d", r.Major, r.Minor, r.Patch)
+}