meta: automatically allow devices as input in the stages schemas

With the new `bootc install to-filesystem` support many stages
will need a devices/mount setup to bind mount the deployment root
from the bootc deployment root of the generated image. To make
this globally available just allow "devices/mounts" for all stages
in the schema validation.

Note that `mounts` is already globally allowed so this just adds
devices (this was added in `7e776a076` with ostree as the use-case).
Nothing will change for the filesystem stages that already define
"devices" in a more specialized way.

osbuild/meta.py

@@ -410,6 +410,11 @@ class ModuleInfo:
                 schema["properties"]["mounts"] = {
                     "type": "array"
                 }
+            if "devices" not in schema["properties"]:
+                schema["properties"]["devices"] = {
+                    "type": "object",
+                    "additionalProperties": True,
+                }
             schema["required"] = [type_id]
         elif self.type in ("Device"):
             schema["additionalProperties"] = True