org.osbuild.ostree.config: Add support for composefs option

The new `composefs` key will, if set, set the `composefs` key
in the `ex-integrity.composefs` configuration section. If set to
true, it means that when deploying from this repository a
composefs image will be created.

A value of `maybe` is also supported, which means composefs will
only be created if support is built into ostree.

Support for this was added in ostree 2023.4, earlier versions ignore
this key.

stages/org.osbuild.ostree.config

@@ -42,6 +42,11 @@ SCHEMA = """
           "readonly": {
             "description": "Read only sysroot and boot",
             "type": "boolean"
+          },
+          "composefs": {
+            "description": "Enable composefs image generation on deploy.",
+            "type": "string",
+            "enum": ["true", "false", "maybe"]
           }
         }
       }
@@ -74,6 +79,10 @@ def main(tree, options):
         ro = "true" if readonly else "false"
         ostree("config", "set", "sysroot.readonly", ro, repo=repo)
 
+    composefs = sysroot_options.get("composefs")
+    if composefs is not None:
+        ostree("config", "set", "ex-integrity.composefs", composefs, repo=repo)
+
 
 if __name__ == '__main__':
     stage_args = osbuild.api.arguments()