System.Text.Json, Shared futures API, Spot websocket V2 API

* Updated CryptoExchange.Net to version 8.0.3, see https://github.com/JKorf/CryptoExchange.Net/releases/tag/8.0.3
* Updated the library to use System.Text.Json for (de)serialization instead of Json.Net
* Updated Spot websocket implementation from V1 to V2
  * Moved requesting of WebSocket token for private endpoints from user endpoint to internal
  * Removed automatic mapping of BTC to XBT (V2 API used BTC as symbol instead of the previous XBT)
  * Respone models have been updated to V2
  * Spread subscription has been removed, part of Ticker stream now
  * Added individual order book subscription
  * Added instrument subscription
  * Added user balances subscription
  * UserTrade subscription has been removed, part of Order stream now
  * Added socketClient.SpotApi.PlaceMultipleOrdersAsync endpoint
  * Added socketClient.SpotApi.EditOrderAsync endpoint
  * Added socketClient.SpotApi.ReplaceOrderAsync endpoint
* Added Shared implementation for Futures WebSocket and REST APIs
* Extended Shared implementation for Spot WebSocket API
* Added restClient.SpotApi.Trading.CancelAllOrdersAfterAsync endpoint
* Added restClient.FuturesApi.ExchangeData.GetTickerAsync endpoint
* Added restClient.FuturesApi.Trading.GetOrdrAync endpoint
* Renamed clientOrderId to userReference parameters in Spot orders as it was implemented with the `userref` field
* Added new clientOrderId parameter to Spot orders using the correct `cl_ord_id` field
* Updated Shared Spot REST implementation to use new clientOrderId property
* Updated restClient.FuturesApi.GetBalancesAsync response so it's more discoverable
* Updated AssetStatus Enum values
* Updated SymbolStatus Enum values
* Fixed deserialization issue FuturesApi.Trading.GetOpenPositionsAsync

Kraken.Net.UnitTests/Endpoints/Futures/Account/GetInitialMarginRequirements.txt

@@ -3,5 +3,5 @@ GET
 true
 {
   "result": "success",
-  "serverTime": "2016-02-25T09:45:53.818Z",
+  "serverTime": "2016-02-25T09:45:53.818Z"
 }

Kraken.Net.UnitTests/Endpoints/Futures/Account/GetMaxOrderQuantity.txt

@@ -3,5 +3,5 @@ GET
 true
 {
   "result": "success",
-  "serverTime": "2016-02-25T09:45:53.818Z",
+  "serverTime": "2016-02-25T09:45:53.818Z"
 }

Kraken.Net.UnitTests/Endpoints/Spot/Trading/CancelAllOrdersAfter.txt

@@ -0,0 +1,10 @@
+POST
+/0/private/CancelAllOrdersAfter
+true
+{
+  "error": [],
+  "result": {
+    "currentTime": "2023-03-24T17:41:56Z",
+    "triggerTime": "2023-03-24T17:42:56Z"
+  }
+}