Drop job step and Create\Update alert handlers (#636)

* Add Delete Job Step implementation

* Update create\update agent alert handlers to use execution handler

* Cleanup create/update/delete operator request handlers

src/Microsoft.SqlTools.ServiceLayer/Agent/Jobs/AgentOperatorActions.cs

@@ -0,0 +1,99 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using Microsoft.SqlTools.ServiceLayer.Agent.Contracts;
+using Microsoft.SqlTools.ServiceLayer.Management;
+
+namespace Microsoft.SqlTools.ServiceLayer.Agent
+{
+    /// <summary>
+    /// Agent Operators management class
+    /// </summary>
+    internal class AgentOperatorActions : ManagementActionBase
+    {
+        private AgentOperatorInfo operatorInfo;
+        private AgentOperatorsData operatorsData = null;
+        private ConfigAction configAction;
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        public AgentOperatorActions(
+            CDataContainer dataContainer, 
+            AgentOperatorInfo operatorInfo,
+            ConfigAction configAction)
+        {
+            if (dataContainer == null)
+            {
+                throw new ArgumentNullException("dataContainer");
+            }
+
+            if (operatorInfo == null)
+            {
+                throw new ArgumentNullException("operatorInfo");
+            }
+
+            this.operatorInfo = operatorInfo;
+            this.DataContainer = dataContainer;
+            this.configAction = configAction;
+
+            STParameters parameters = new STParameters();
+            parameters.SetDocument(dataContainer.Document);
+
+            string agentOperatorName = null;
+            if (parameters.GetParam("operator", ref agentOperatorName))
+            {
+                this.operatorsData = new AgentOperatorsData(
+                    dataContainer, 
+                    agentOperatorName, 
+                    createMode: configAction == ConfigAction.Create);
+            }
+            else
+            {
+                throw new ArgumentNullException("agentOperatorName");
+            }
+        }
+
+        /// <summary> 
+        /// Clean up any resources being used.
+        /// </summary>
+        protected override void Dispose(bool disposing)
+        {
+            if(disposing)
+            {    
+            }
+            base.Dispose(disposing);
+        }
+
+        // <summary>
+        /// called by PreProcessExecution to enable derived classes to take over execution
+        /// </summary>
+        /// <param name="runType"></param>
+        /// <param name="executionResult"></param>
+        /// <returns>
+        /// true if regular execution should take place, false if everything,
+        /// has been done by this function
+        /// </returns>
+        protected override bool DoPreProcessExecution(RunType runType, out ExecutionMode executionResult)
+        {
+            base.DoPreProcessExecution(runType, out executionResult);
+
+            if (this.configAction == ConfigAction.Drop)
+            {
+                var currentOperator = this.operatorsData.Operator;
+                if (currentOperator != null)
+                {
+                    currentOperator.DropIfExists();
+                }
+            }
+            else
+            {
+                this.operatorsData.ApplyChanges(this.operatorInfo);
+            }
+            return false;
+        }
+    }
+}