feat: allowed to set retryBackOff parameter of FailJobCommand

Client.UnitTests/FailJobTest.cs

@@ -20,11 +20,16 @@ public async Task ShouldSendRequestAsExpected()
             {
                 JobKey = jobKey,
                 ErrorMessage = errorMessage,
-                Retries = 2
+                Retries = 2,
+                RetryBackOff = 1562
             };
 
             // when
-            await ZeebeClient.NewFailCommand(jobKey).Retries(2).ErrorMessage("This job failed!").Send();
+            await ZeebeClient.NewFailCommand(jobKey)
+                .Retries(2)
+                .ErrorMessage("This job failed!")
+                .RetryBackOff(TimeSpan.FromMilliseconds(1562.5))
+                .Send();
 
             // then
             var actualRequest = TestService.Requests[typeof(FailJobRequest)][0];

Client/Api/Commands/IFailJobCommandStep1.cs

@@ -12,6 +12,7 @@
 //    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 //    See the License for the specific language governing permissions and
 //    limitations under the License.
+using System;
 using Zeebe.Client.Api.Responses;
 
 namespace Zeebe.Client.Api.Commands
@@ -47,5 +48,16 @@ public interface IFailJobCommandStep2 : IFinalCommandWithRetryStep<IFailJobRespo
         ///     to the broker.
         ///     </returns>
         IFailJobCommandStep2 ErrorMessage(string errorMsg);
+
+        /// <summary>
+        /// Set the backoff timeout for the next retry of this job.
+        ///
+        /// </summary>
+        ///
+        /// <param name="retryBackOff">the backoff timeout for the next retry of this job.</param>
+        /// <returns>the builder for this command. Call <see cref="IFinalCommandStep{T}.Send"/> to complete the command and send it
+        ///     to the broker.
+        /// </returns>
+        IFailJobCommandStep2 RetryBackOff(TimeSpan retryBackOff);
     }
 }

Client/Impl/Commands/FailJobCommand.cs

@@ -53,6 +53,12 @@ public IFailJobCommandStep2 ErrorMessage(string errorMsg)
             return this;
         }
 
+        public IFailJobCommandStep2 RetryBackOff(TimeSpan retryBackOff)
+        {
+            request.RetryBackOff = (long)retryBackOff.TotalMilliseconds;
+            return this;
+        }
+
         public async Task<IFailJobResponse> Send(TimeSpan? timeout = null, CancellationToken token = default)
         {
             var asyncReply = gatewayClient.FailJobAsync(request, deadline: timeout?.FromUtcNow(), cancellationToken: token);