(data): Add version function to schema.

data/schema.sql

@@ -17,6 +17,18 @@ BEGIN
 END;
 $$ language 'plpgsql';
 
+CREATE OR REPLACE FUNCTION current_module_version(module_name TEXT)
+RETURNS INTEGER
+AS $$
+    SELECT 
+      to_version 
+    FROM version_history 
+    WHERE 
+      component = $1 
+    ORDER BY _timestamp DESC 
+    LIMIT 1;
+$$ LANGUAGE SQL;
+
 CREATE TABLE app_config(
   appname TEXT PRIMARY KEY,
   created_at TIMESTAMPTZ NOT NULL DEFAULT now()