Add downstream test config

This will cause coin to test the newly integrated HEAD for the
given modules. In case a failure occurs in the check a message
in gerrit is sent to the commits which were integrated in the
HEAD.

Change-Id: I656316c7cceb126ccf570fd3db3f7fd2b22cc4fa
Reviewed-by: Simo Fält <simo.falt@qt.io>

coin/module_config.yaml

@@ -4,6 +4,14 @@ accept_configuration:
   property: features
   not_contains_value: Disable
 
+downstream_check:
+  mode: build
+  modules:
+    ../qtdeclarative:
+      ref: dev
+  configurations:
+    - rhel-8.4
+
 machine_type:
   Build:
     cores: 8