schemas/osbuild2: mark version as required

The v2 manifest requires the `version` key to be present to be
distinguishable from v1. While technically the manifest can be used
standalong without a `version` key, it does prevent us implementing the
manifest correctly in osbuild (i.e., we are unable to process a v2
manifest without the `version` key, because we are unable to autodetect
it then).

Mark the key as required. It does kind of break backwards compatibility
of the schema, but at the same time we always treated it this way,
anyway. So this should be fine.

Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>

schemas/osbuild2.json

@@ -6,6 +6,7 @@
   "description": "OSBuild manifest describing a pipeline and all parameters",
   "type": "object",
   "additionalProperties": false,
+  "required": ["version"],
   "properties": {
     "pipelines": { "$ref": "#/definitions/pipelines" },
     "sources": { "$ref": "#/definitions/sources" },