feat: update ref schema

Author: dancixx

schemas/reference.surql

@@ -14,3 +14,4 @@ DEFINE FIELD OVERWRITE created_at ON reference TYPE datetime DEFAULT time::now()
 DEFINE FIELD OVERWRITE updated_at ON reference TYPE datetime VALUE time::now();
 DEFINE FIELD OVERWRITE category ON reference TYPE string;
 DEFINE FIELD OVERWRITE year ON reference TYPE int;
+DEFINE FIELD OVERWRITE icon ON reference TYPE string;