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/docker/go-units/MAINTAINERS

@@ -0,0 +1,46 @@
+# go-units maintainers file
+#
+# This file describes who runs the docker/go-units project and how.
+# This is a living document - if you see something out of date or missing, speak up!
+#
+# It is structured to be consumable by both humans and programs.
+# To extract its contents programmatically, use any TOML-compliant parser.
+#
+# This file is compiled into the MAINTAINERS file in docker/opensource.
+#
+[Org]
+	[Org."Core maintainers"]
+		people = [
+			"akihirosuda",
+			"dnephin",
+			"thajeztah",
+			"vdemeester",
+		]
+
+[people]
+
+# A reference list of all people associated with the project.
+# All other sections should refer to people by their canonical key
+# in the people section.
+
+	# ADD YOURSELF HERE IN ALPHABETICAL ORDER
+
+	[people.akihirosuda]
+	Name = "Akihiro Suda"
+	Email = "akihiro.suda.cz@hco.ntt.co.jp"
+	GitHub = "AkihiroSuda"
+
+	[people.dnephin]
+	Name = "Daniel Nephin"
+	Email = "dnephin@gmail.com"
+	GitHub = "dnephin"
+	
+	[people.thajeztah]
+	Name = "Sebastiaan van Stijn"
+	Email = "github@gone.nl"
+	GitHub = "thaJeztah"
+
+	[people.vdemeester]
+	Name = "Vincent Demeester"
+	Email = "vincent@sbr.pm"
+	GitHub = "vdemeester"