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/containers/image/v5/internal/tmpdir/tmpdir.go

@@ -0,0 +1,34 @@
+package tmpdir
+
+import (
+	"os"
+	"runtime"
+
+	"github.com/containers/image/v5/types"
+)
+
+// unixTempDirForBigFiles is the directory path to store big files on non Windows systems.
+// You can override this at build time with
+// -ldflags '-X github.com/containers/image/v5/internal/tmpdir.unixTempDirForBigFiles=$your_path'
+var unixTempDirForBigFiles = builtinUnixTempDirForBigFiles
+
+// builtinUnixTempDirForBigFiles is the directory path to store big files.
+// Do not use the system default of os.TempDir(), usually /tmp, because with systemd it could be a tmpfs.
+// DO NOT change this, instead see unixTempDirForBigFiles above.
+const builtinUnixTempDirForBigFiles = "/var/tmp"
+
+// TemporaryDirectoryForBigFiles returns a directory for temporary (big) files.
+// On non Windows systems it avoids the use of os.TempDir(), because the default temporary directory usually falls under /tmp
+// which on systemd based systems could be the unsuitable tmpfs filesystem.
+func TemporaryDirectoryForBigFiles(sys *types.SystemContext) string {
+	if sys != nil && sys.BigFilesTemporaryDir != "" {
+		return sys.BigFilesTemporaryDir
+	}
+	var temporaryDirectoryForBigFiles string
+	if runtime.GOOS == "windows" {
+		temporaryDirectoryForBigFiles = os.TempDir()
+	} else {
+		temporaryDirectoryForBigFiles = unixTempDirForBigFiles
+	}
+	return temporaryDirectoryForBigFiles
+}