TD-933: Adds support for deviation direction for amount randomization (#93)

spec/definitions/InvoiceRandomizeAmount.yaml

@@ -26,6 +26,15 @@ properties:
     minimum: 0
     maximum: 5
     default: 2
+  direction:
+    description: >
+      Direction of deviation from original amount.
+    type: string
+    default: both
+    enum:
+      - both
+      - upward
+      - downward
   minAmountCondition:
     description: >
       Minimum amount applicable for randomization, in minor monetary