Limit concurrent HTTP requests with SemaphoreSlim

Introduced a `SemaphoreSlim` with a concurrency limit of 5 to
control the number of simultaneous HTTP requests. Updated the
HTTP request logic to use `WaitAsync` and `Release` for
managing access to the critical section. Wrapped the HTTP
request handling in a `try-finally` block to ensure proper
semaphore release, even in case of exceptions. This change
improves resource management and prevents overwhelming the
HTTP client or the target server.

src/ReC.Application/RecActions/Commands/InvokeRecActionCommand.cs

@@ -21,7 +21,12 @@ public class InvokeRecActionCommandHandler(ISender sender, IHttpClientFactory cl
 
         var http = clientFactory.CreateClient();
 
+        using var semaphore = new SemaphoreSlim(5);
+
         var tasks = actions.Select(async action =>
+        {
+            await semaphore.WaitAsync(cancel);
+            try
             {
                 var method = new HttpMethod(action.RestType.ToUpper());
                 var msg = new HttpRequestMessage(method, action.EndpointUri);
@@ -29,6 +34,11 @@ public class InvokeRecActionCommandHandler(ISender sender, IHttpClientFactory cl
                 var response = await http.SendAsync(msg, cancel);
                 var body = await response.Content.ReadAsStringAsync(cancel);
                 var headers = response.Headers.ToDictionary();
+            }
+            finally
+            {
+                semaphore.Release();
+            }
         });
 
         await Task.WhenAll(tasks);