schema: support multiple images destinations

In coreos/fedora-coreos-pipeline#1091 we added
the possibility of publishing container images to multiples repositories.

This needs to be reflected in the schema otherwhise we only record one
image (currenlty the last pushed).

Add a `primary-image` key that extends image by adding an `additional-images`
array.

Use that for relevant container images objects.

See coreos/fedora-coreos-pipeline#1099

Author: jbtrystram

src/v1.json

@@ -85,6 +85,20 @@
         }
       }
     },
+    "primary-image": {
+      "type": "object",
+      "extends": "#/image",
+      "optional": [
+        "additional-images"
+      ],
+      "properties": {
+        "additional-images": {
+          "$id": "#/image",
+          "type": "array",
+          "title": "Additional images"
+        }
+      }
+    },
     "cloudartifact": {
       "type": "object",
       "required": [
@@ -702,7 +716,7 @@
       "$id": "#/properties/oscontainer",
       "type": "object",
       "title": "Oscontainer",
-      "$ref": "#/definitions/image"
+      "$ref": "#/definitions/primary-image"
     },
     "extensions": {
       "$id": "#/properties/extensions",
@@ -921,13 +935,13 @@
       "$id": "#/properties/base-oscontainer",
       "type": "object",
       "title": "Base OS container",
-      "$ref": "#/definitions/image"
+      "$ref": "#/definitions/primary-image"
     },
     "extensions-container": {
       "$id": "#/properties/extensions-container",
       "type": "object",
       "title": "Extensions container",
-      "$ref": "#/definitions/image"
+      "$ref": "#/definitions/primary-image"
     },
     "gcp": {
       "$id": "#/properties/gcp",
@@ -968,7 +982,7 @@
       "$id": "#/properties/kubevirt",
       "type": "object",
       "title": "Kubevirt container",
-      "$ref": "#/definitions/image"
+      "$ref": "#/definitions/primary-image"
     },
     "ibmcloud": {
       "$id": "#/properties/ibmcloud",