Mattoni/new invoice state (#479)

* Add the 'awaiting-funds' invoice state

* fix invoice state update

* remove from events

* fix description

Author: mattoni

components/schemas/billing/invoices/Invoice.yml

@@ -63,7 +63,6 @@ properties:
       - updated
       - deleted
       - billed
-      - awaiting-funds
       - paid
       - credited
       - voided

components/schemas/billing/invoices/InvoiceState.yml

@@ -4,14 +4,15 @@ allOf:
       - current
     properties:
       current:
-        description: The current state of the container.
+        description: The current state of the invoice.
         type: string
         enum:
           - "new"
           - "billing"
           - "billed"
           - "processing"
           - "partially-paid"
+          - "awaiting-funds"
           - "paid"
           - "refunding"
           - "refunded"