cloudapi: support container embedding

Add support for embedding container images via the cloud API. For
this the container resolve job was plumbed into the cloud api's
handler and the API specification updated with a new `containers`
section that mimics the blueprint section with the same name.

internal/cloudapi/v2/openapi.v2.yml

@@ -859,6 +859,11 @@ components:
     Customizations:
       type: object
       properties:
+        containers:
+          type: array
+          items:
+             $ref: '#/components/schemas/Container'
+             description: Container images to embed into the final artfact
         subscription:
           $ref: '#/components/schemas/Subscription'
         packages:
@@ -902,6 +907,22 @@ components:
               items:
                 type: string
                 example: "firewalld"
+    Container:
+      type: object
+      required:
+        - source
+      properties:
+        source:
+          type: string
+          desription: Reference to the container to embed
+          example: 'registry.example.com/image:tag'
+        name:
+          type: string
+          description: Name to use for the container from the image
+        tls_verify:
+          type: boolean
+          description: Control TLS verifification
+          example: true
     Filesystem:
       type: object
       required: