Victoria: Add releasenote for remove congress role

The congress project is no longer maintained. This has been
retired since Victoria[1] and has not been used by other OpenStack
services since.

[1]: http://lists.openstack.org/pipermail/openstack-discuss/2020-April/014292.html

Depends-On: I21c9ab9820f78cf76adf11c5f0591c60f76372a8
Change-Id: I561ead226f714d98c8e06e6027715a64c3a8e47e

releasenotes/notes/remove-congress-role-0f6a327de69e2173.yaml

+---
+deprecations:
+  - |
+    The ``congress`` project is no longer maintained. This has been
+    `retired since Victoria`__ and has not been used by other OpenStack
+    services since.
+
+    __ http://lists.openstack.org/pipermail/openstack-discuss/2020-April/014292.html