Update git submodules

* Update docs/submodules/opera from branch 'stable/danube'
  - Add scenario description in docs

    Change-Id: Ifc78defa03099c284995108f9d00315bbff2495a
    Signed-off-by: Harry Huang <huangxiangyu5@huawei.com>
    (cherry picked from commit 01ff8987aa2b1439a02712f4bb501c704287309e)

diff --git a/docs/submodules/opera b/docs/submodules/opera
index 82de7c1..12b839c 160000 (submodule)
--- a/docs/submodules/opera
+++ b/docs/submodules/opera
@@ -1 +1 @@
-Subproject commit 82de7c1f69ad128ee9f60aae271c54dd69fc8c22
+Subproject commit 12b839c18d26d44b76de29c682d5fa25b086fde7