add ability to configure MaxTasks in SelectorOptions

Author: TechnoBerry

src/Camunda.Worker/Execution/ExternalTaskSelector.cs

@@ -56,7 +56,7 @@ private FetchAndLockRequest MakeRequestBody()
         {
             var topics = _topicsProvider.GetTopics();
 
-            var fetchAndLockRequest = new FetchAndLockRequest(_workerOptions.WorkerId)
+            var fetchAndLockRequest = new FetchAndLockRequest(_workerOptions.WorkerId, _selectorOptions.MaxTasks)
             {
                 UsePriority = _selectorOptions.UsePriority,
                 AsyncResponseTimeout = _selectorOptions.AsyncResponseTimeout,

src/Camunda.Worker/Execution/SelectorOptions.cs

@@ -2,8 +2,15 @@ namespace Camunda.Worker.Execution
 {
     public class SelectorOptions
     {
+        private int _maxTasks = 1;
         private int _asyncResponseTimeout = 10_000;
 
+        public int MaxTasks
+        {
+            get => _maxTasks;
+            set => _maxTasks = Guard.GreaterThanOrEqual(value, 1, nameof(MaxTasks));
+        }
+
         public int AsyncResponseTimeout
         {
             get => _asyncResponseTimeout;