Add Agent Job and Job Step request handlers (#635)

* Stage changes

* Fix update job request handler

* WIP

* Additional agent handler updates

* Setup agent job step create test

* Fix Step update handler

src/Microsoft.SqlTools.ServiceLayer/DisasterRecovery/DisasterRecoveryService.cs

@@ -13,6 +13,7 @@ using Microsoft.SqlTools.ServiceLayer.Connection.Contracts;
 using Microsoft.SqlTools.ServiceLayer.DisasterRecovery.Contracts;
 using Microsoft.SqlTools.ServiceLayer.DisasterRecovery.RestoreOperation;
 using Microsoft.SqlTools.ServiceLayer.FileBrowser;
+using Microsoft.SqlTools.ServiceLayer.Management;
 using Microsoft.SqlTools.ServiceLayer.TaskServices;
 using Microsoft.SqlTools.Utility;