Accounts updated subscription

[Victor-N-Suadicani]

Purpose

I'm honestly not sure where this is used in the frontend.

Changes

Added the AccountsUpdatedSubscriptionItem and the appropriate methods to Subscription, which are largely inspired by the already-existing block_added subscription.

What's missing is actually sending the notifications when the appropriate event happens - this is left for future work.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[DOBEN]

The AccountsUpdatedSubscription is used as part of the web socket connection when the accounts page view is open e.g.
https://testnet.ccdscan.io/?dcount=1&dentity=account&daddress=4dT5vPrnnpwVrXZgmYLtHrDLvBYhtzheaK4fDWbJewqRCGQKWz

You can open the network tab and click on the ws tab to explore the web socket connections in the DevTools in the browser.

[DOBEN]

The query at the front-end includes an additional accountAddress query variable:

{
    "id": "1",
    "type": "start",
    "payload": {
        "key": "...",
        "query": "subscription accountsUpdatedSubscription($accountAddress: String!) {\n  accountsUpdated(accountAddress: $accountAddress) {\n    address\n  }\n}",
        "variables": {
            "accountAddress": "4dT5vPrnnpwVrXZgmYLtHrDLvBYhtzheaK4fDWbJewqRCGQKWz"
        },
        "context": {
            "url": "https://api-ccdscan.testnet.concordium.com/graphql",
            "preferGetMethod": false,
            "suspense": false,
            "requestPolicy": "cache-first",
            "meta": {
                "cacheOutcome": "miss"
            }
        }
    }
}

[Victor-N-Suadicani]

Right - but what am I supposed to do with that input string? 🤔

In the C# code, it seems it's the "topic" of the subscription? Not sure what that means.

public class Subscription
{
    [Subscribe]
    [Topic("{accountAddress}")]
    public AccountsUpdatedSubscriptionItem AccountsUpdated(
        string accountAddress, 
        [EventMessage] AccountsUpdatedSubscriptionItem message) => message;

    [Subscribe]
    public Block BlockAdded([EventMessage] Block block) => block;
}