Get a subscription measurement.

curl -X GET \
 /subscription-measurements/{id} \
 --header "Authorization: Bearer <token>"

{
  "id": "ad8f1c2c-3b1c-4b0a-8b0a-0b0b0b0b0b0b",
  "subscriptionItem": "https://example.com/",
  "measurement": "https://example.com/",
  "quantity": 1,
  "measuredAt": "2021-01-01T00:00:00+00:00",
  "tenantId": "<string>"
}