Add billing_source to Account schema

openapi.yaml

@@ -19238,6 +19238,19 @@ components:
             the estimate.
           example: 145
           x-linode-cli-display: 4
+        billing_source:
+          type: string
+          readOnly: true
+          enum:
+            - akamai
+            - linode
+          description: >
+            The source of service charges for this Account, as determined by its relationship with Akamai.
+
+            Accounts that are associated with Akamai-specific customers return a value of `akamai`.
+
+            All other Accounts return a value of `linode`.
+          example: akamai
         capabilities:
           type: array
           items: