cloudapi: Add optional image size support

This adds a 'size' parameter to the image_request object. It can be used
to specify the minimum image size in bytes

This behaves in the same way as the size parameter of the weldr API

For raw images the root partition is grown to fill the available space.
For LVM images the PV uses the available space, but the LV does not,
leaving space available for other LVs to be created after boot.

See COMPOSER-1883

internal/cloudapi/v2/openapi.v2.yml

@@ -760,6 +760,13 @@ components:
           $ref: '#/components/schemas/OSTree'
         upload_options:
           $ref: '#/components/schemas/UploadOptions'
+        size:
+          x-go-type: uint64
+          default: 0
+          example: 4294967296
+          description: |
+            Size of image, in bytes. When set to 0 the image size is a minimum
+            defined by the image type.
     ImageTypes:
       type: string
       enum:
@@ -1200,7 +1207,8 @@ components:
           example: '/var'
         min_size:
           x-go-type: uint64
-          example: 1024
+          example: 2147483648
+          description: 'size of the filesystem in bytes'
     OSTree:
       type: object
       properties: