cmd-import: add coreos-assembler.container-image-git to meta.json

That key contains information about the cosa container image itself
being used. There's some value in capturing this even just for knowing
what `cosa import` code was executed, but it's also much more important
when we talk about the disk images, which still heavily rely on cosa
code.

This should make the "COSA commit" key show up in the build browser.

Author: jlebon

src/cmd-import

@@ -154,6 +154,14 @@ def generate_build_meta(tmp_oci_archive, tmp_oci_manifest, metadata, ostree_comm
             'commit': commit,
         }
 
+    # add a reference to ourselves as well
+    try:
+        with open('/cosa/coreos-assembler-git.json') as f:
+            cosa_git = json.load(f)
+            meta['coreos-assembler.container-image-git'] = cosa_git['git']
+    except FileNotFoundError:
+        pass
+
     return meta