core: Allow adding related objects to commits

This will be used to store the set of components.

src/libostree/ostree-repo.c

@@ -1691,6 +1691,7 @@ ostree_repo_stage_commit (OstreeRepo *self,
                           const char   *subject,
                           const char   *body,
                           GVariant     *metadata,
+                          GVariant     *related_objects,
                           const char   *root_contents_checksum,
                           const char   *root_metadata_checksum,
                           char        **out_commit,
@@ -1712,8 +1713,7 @@ ostree_repo_stage_commit (OstreeRepo *self,
   commit = g_variant_new ("(@a{sv}@ay@a(say)sst@ay@ay)",
                           metadata ? metadata : create_empty_gvariant_dict (),
                           parent ? ostree_checksum_to_bytes_v (parent) : ot_gvariant_new_bytearray (NULL, 0),
-                          g_variant_new_array (G_VARIANT_TYPE ("(say)"),
-                                               NULL, 0),
+                          related_objects ? related_objects : g_variant_new_array (G_VARIANT_TYPE ("(say)"), NULL, 0),
                           subject, body ? body : "",
                           GUINT64_TO_BE (g_date_time_to_unix (now)),
                           ostree_checksum_to_bytes_v (root_contents_checksum),