Update git submodules

* Update docs/submodules/apex from branch 'stable/euphrates'
  - Freezes RDO images for Euphrates

    Change-Id: Ie20e7d0c52efc2497c7c9975f88be0a9bfa7aa07
    Signed-off-by: Tim Rozet <trozet@redhat.com>

diff --git a/docs/submodules/apex b/docs/submodules/apex
index ea691fe..f6792ad 160000 (submodule)
--- a/docs/submodules/apex
+++ b/docs/submodules/apex
@@ -1 +1 @@
-Subproject commit ea691fed3042f42701cb355ce1db305564ba229a
+Subproject commit f6792ad2fff60fae3759eaf7d4092012acf360db