chore(model): add model table for jobs

models/jobsystem.model

@@ -1,5 +1,17 @@
--- Jobs to be fetched and distributed to the workers by the scheduler
+-- Metadata of jobs to be fetched by the scheduler and to be
+-- assigned to the workers
 -- part of the *new* job system
 JobMeta
-  occurrence JobOccurrence  -- when should the job be executed? (Possibly recurring)
+  occurrence JobOccurrence  -- When should the job be executed?
+                            -- (Possibly recurring)
+  deriving Eq Ord Show Generic
+
+-- Actual job to be fetched and executed by the workers
+-- part of the *new* job system
+JobData
+  meta       JobMetaId
+  content    Value  -- JSON representation of the job content
+                    -- (parsing as generic Aeson Value 
+                    --  instead of Job for compatibility with 
+                    --  legacy jobs)
   deriving Eq Ord Show Generic