chore(system-msgs): add volatile cluster settings to db

models/system-messages.model

@@ -1,8 +1,9 @@
 -- Messages shown to all users as soon as they visit the site/log in (i.e.: "System is going down for maintenance next sunday")
 -- Only administrators (of any school) should be able to create these via a web-interface
-SystemMessage
+SystemMessage json
     from                UTCTime Maybe -- Message is not shown before this date has passed (never shown, if null)
     to                  UTCTime Maybe -- Message is shown until this date has passed (shown forever, if null)
+    onVolatileClusterSettings SystemMessageVolatileClusterSettings -- Message is shown when given volatile cluster settings have given values
     newsOnly            Bool default=false
     authenticatedOnly   Bool -- Show message to all users upon visiting the site or only upon login?
     severity            MessageStatus -- Success, Warning, Error, Info, ...

src/Model/Types.hs

@@ -25,3 +25,4 @@ import Model.Types.Room as Types
 import Model.Types.Csv as Types
 import Model.Types.Upload as Types
 import Model.Types.Communication as Types
+import Model.Types.SystemMessage as Types

src/Model/Types/SystemMessage.hs

@@ -0,0 +1,6 @@
+module Model.Types.SystemMessage where
+
+import Import.NoModel
+
+
+type SystemMessageVolatileClusterSettings = Set (VolatileClusterSettingsKey, Value)