Seaparate CoinSwitch as a plugin (#2390)

* Separate coinswitch as a system plugin

* Decouple Coinswitch from Checkout UI

* remove dummy csproj

* Remove CoinSwitchTests.cs per @NicolasDorier feedback

Co-authored-by: rockstardev <rockstardev@users.noreply.github.com>

BTCPayServer/Plugins/CoinSwitch/UpdateCoinSwitchSettingsViewModel.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNetCore.Mvc.Rendering;
+
+namespace BTCPayServer.Models.StoreViewModels
+{
+    public class UpdateCoinSwitchSettingsViewModel
+    {
+        public string MerchantId { get; set; }
+        public bool Enabled { get; set; }
+
+        [Display(Name = "Integration Mode")]
+        public string Mode { get; set; } = "inline";
+
+        [Required]
+        [Range(0, 100)]
+        [Display(Name =
+            "Percentage to multiply amount requested at Coinswitch to avoid underpaid situations due to Coinswitch not guaranteeing rates. ")]
+        public decimal AmountMarkupPercentage { get; set; } = new decimal(2);
+
+        public List<SelectListItem> Modes { get; } = new List<SelectListItem>
+        {
+            new SelectListItem { Value = "popup", Text = "Open in a popup" },
+            new SelectListItem { Value = "inline", Text = "Embed inside Checkout UI " },
+        };
+    }
+}