Proposal: Show description and interval of canceled subscriptions

[ipr0310]

As a subscription platform, we should also consider showing the description and interval of expired/cancelled subscriptions
The current way to fetch expired/canceled subscriptions is by fetching the transactions with type=21 and subtype=4

As you can see on the response payload, the attachment property. description and interval is missing.

{
      "type": 21,
      "subtype": 4,
      "timestamp": 278363698,
      "deadline": 1440,
      "senderPublicKey": "7158e2e1170f9a3e1799ba4069ab55fac3d2242db5c0a08faf91c8b7cac3cb1f",
      "amountNQT": "0",
      "feeNQT": "2000000",
      "signature": "b3db293e1fe637feda63ad9229cb3d6fbfa3afb4b6f104dd2b1c90e0d093130378d8acc6f7add947cebbc669d24ffbd700909f506376529b1cc117ebeb0e1e7f",
      "signatureHash": "d5cc652417775a8ff35a9b9845b1b389eefeb9012684e2cc297c7a32cebb5a24",
      "fullHash": "db68ec363e0b6e2af925056151ae37da50c2a0d843652730dd035ead5c9dc56d",
      "transaction": "3057393558868486363",
      "attachment": {
        "version.SubscriptionCancel": 1,
        "subscriptionId": "10561777840324094517"
      },
   // ...Remaining Transaction objects
    }

It means the only way of getting the description and interval of canceled subscriptions is by making another getTransaction request.

Suggestion:
We can consider extending the attachment property

    "attachment": {
        "version.SubscriptionCancel": 1,
        "subscriptionId": "10561777840324094517",
        "subscriptionDescription": "SRC44 DESCRIPTION OF CANCELLED SUBSCRIPTION",
        "subscriptionInterval": "0000000",
     }

Benefits:

• Prevents unnecessary requests
• Save bandwidth