Update git submodules

* Update docs/submodules/fuel from branch 'stable/euphrates'
  - Update release notes for 5.1

    The release notes are updated with relevant Jira filters and
    changes since 5.0

    Change-Id: If14cb0369ced899d17608ef43e93b848e8b2a5c8
    Signed-off-by: Cristina Pauna <cristina.pauna@enea.com>
    (cherry picked from commit fcb2fd879b9770bc5dd84507895be7d58f02d4ae)

diff --git a/docs/submodules/fuel b/docs/submodules/fuel
index d9c4d13..7020f4a 160000 (submodule)
--- a/docs/submodules/fuel
+++ b/docs/submodules/fuel
@@ -1 +1 @@
-Subproject commit d9c4d1311a585f56e5e4ca62d4415581ab21759e
+Subproject commit 7020f4a880f0b7a5d8941da4001061dcc9c56793