add csharp snippets

snippets/csharp/SendOnchain.cs

@@ -0,0 +1,72 @@
+using Breez.Sdk;
+
+public class SendOnchainSnippets
+{
+    public void GetCurrentFees(BlockingBreezServices sdk)
+    {
+        // ANCHOR: estimate-current-reverse-swap-total-fees
+        try
+        {
+            var currentFees = sdk.FetchReverseSwapFees(
+                new ReverseSwapFeesRequest(50000));
+            Console.WriteLine(
+                $"Total estimated fees for reverse " +
+                $"swap: {currentFees.totalEstimatedFees}");
+        }
+        catch (Exception)
+        {
+            // Handle error
+        }
+        // ANCHOR_END: estimate-current-reverse-swap-total-fees
+    }
+
+    public void ListCurrentFees(BlockingBreezServices sdk, ReverseSwapPairInfo currentFees)
+    {
+        // ANCHOR: get-current-reverse-swap-min-max
+        Console.WriteLine($"Minimum amount, in sats: {currentFees.min}");
+        Console.WriteLine($"Maximum amount, in sats: {currentFees.max}");
+        // ANCHOR_END: get-current-reverse-swap-min-max
+    }
+
+    public void StartReverseSwap(BlockingBreezServices sdk, ReverseSwapPairInfo currentFees, uint feeRate)
+    {
+        // ANCHOR: start-reverse-swap
+        var destinationAddress = "bc1..";
+        var amountSat = currentFees.min;
+        var satPerVbyte = feeRate;
+        try
+        {
+            var reverseSwapInfo = sdk.SendOnchain(
+                new SendOnchainRequest(
+                    amountSat,
+                    destinationAddress,
+                    currentFees.feesHash,
+                    satPerVbyte));
+        }
+        catch (Exception)
+        {
+            // Handle error
+        }
+        // ANCHOR_END: start-reverse-swap
+    }
+
+    public void CheckReverseSwapStatus(BlockingBreezServices sdk)
+    {
+        // ANCHOR: check-reverse-swaps-status
+        try
+        {
+            var swaps = sdk.InProgressReverseSwaps();
+            foreach (var swap in swaps)
+            {
+                Console.WriteLine(
+                    $"Reverse swap {swap.id} in progress, " +
+                    $"status is {swap.status}`");
+            }
+        }
+        catch (Exception)
+        {
+            // Handle error
+        }
+        // ANCHOR_END: check-reverse-swaps-status
+    }
+}