Introduce cloud-base sample

It is similar to the official Fedora cloud base image except for few
minor differences. The reason for this divergence is that we don't want
to include all hacks that are currently present in the official
kickstart file. You can see it here as a reference:
https://pagure.io/fedora-kickstarts/blob/master/f/fedora-cloud-base.ks#_149

samples/cloud-base.json

@@ -0,0 +1,83 @@
+{
+  "stages": [
+    {
+      "name": "org.osbuild.dnf",
+      "options": {
+        "releasever": "30",
+        "basearch": "x86_64",
+        "install_weak_deps": true,
+        "repos": [
+          {
+            "metalink": "https://mirrors.fedoraproject.org/metalink?repo=fedora-$releasever&arch=$basearch",
+            "gpgkey": "F1D8 EC98 F241 AAF2 0DF6  9420 EF3C 111F CFC6 59B9",
+            "checksum": "sha256:9f596e18f585bee30ac41c11fb11a83ed6b11d5b341c1cb56ca4015d7717cb97"
+          }
+        ],
+        "packages": [
+          "kernel-core",
+	  "@Fedora Cloud Server",
+	  "chrony",
+	  "polkit",
+	  "systemd-udev",
+          "selinux-policy-targeted",
+          "grub2-pc",
+          "langpacks-en"
+        ],
+        "exclude_packages": [
+          "dracut-config-rescue",
+	  "etables",
+	  "firewalld",
+	  "gobject-introspection",
+	  "plymouth"
+        ]
+      }
+    },
+    {
+      "name": "org.osbuild.locale",
+      "options": {
+        "language": "en_US"
+      }
+    },
+    {
+      "name": "org.osbuild.fstab",
+      "options": {
+        "filesystems": [
+          {
+            "uuid": "ea711a29-e460-4879-9d70-9da99ae021f9",
+            "vfs_type": "ext4",
+            "path": "/",
+            "freq": "1",
+            "passno": "1"
+          }
+        ]
+      }
+    },
+    {
+      "name": "org.osbuild.grub2",
+      "options": {
+        "root_fs_uuid": "ea711a29-e460-4879-9d70-9da99ae021f9",
+        "kernel_opts": "ro biosdevname=0 net.ifnames=0"
+      }
+    },
+    {
+      "name": "org.osbuild.selinux",
+      "options": {
+        "file_contexts": "etc/selinux/targeted/contexts/files/file_contexts"
+      }
+    },
+    {
+      "name": "org.osbuild.fix-bls"
+    }
+  ],
+  "assembler":
+    {
+      "name": "org.osbuild.qemu",
+      "options": {
+        "format": "qcow2",
+        "filename": "base.qcow2",
+        "ptuuid": "0x14fc63d2",
+        "root_fs_uuid": "ea711a29-e460-4879-9d70-9da99ae021f9",
+        "size": 3221225472
+      }
+    }
+}