assemblers/ostree.commit: report compose metadata

Pass all the compose metadata, as given by rpm-ostree via the
compose.json, back to osbuild via the new api.metadata method.

assemblers/org.osbuild.ostree.commit

@@ -25,6 +25,7 @@ import subprocess
 import sys
 import tempfile
 
+from osbuild import api
 from osbuild.util import ostree
 
 
@@ -162,6 +163,11 @@ def main(tree, output_dir, options, meta):
                            stdout=sys.stderr,
                            check=True)
 
+        with open(os.path.join(output_dir, "compose.json"), "r") as f:
+            compose = json.load(f)
+
+        api.metadata({"compose": compose})
+
     if tar:
         filename = tar["filename"]
         command = [