Prepare new stable/yoga release

This is a convenience patch related to convenience releases proposed
recently [1].

[1] https://review.opendev.org/q/topic:yoga-convenience-before-em

Change-Id: Iea1bb7936e5edc6da80df1df2e1b83a459e19d65

metadata.json

@@ -54,5 +54,5 @@
     ],
     "source": "https://opendev.org/openstack/puppet-ovn.git",
     "summary": "Modules to setup ovn-northd and ovn-controller",
-    "version": "20.3.0"
+    "version": "20.4.0"
 }