Added flush conn to nsg (#18393)

* Added flush conn to nsg

* Updated flushConn to correct location

* Updated description

* Modified T/F to Enabled/Disabled

* Refactoring so that null value appears first

* Reverted FlushConnection to boolean value instead of string

Author: Satya-anshu

specification/network/resource-manager/Microsoft.Network/stable/2021-08-01/examples/NetworkSecurityGroupCreate.json

@@ -17,6 +17,7 @@
         "location": "eastus",
         "properties": {
           "provisioningState": "Succeeded",
+          "flushConnection": false,
           "securityRules": [],
           "defaultSecurityRules": [
             {
@@ -127,6 +128,7 @@
         "location": "eastus",
         "properties": {
           "provisioningState": "Succeeded",
+          "flushConnection": false,
           "securityRules": [],
           "defaultSecurityRules": [
             {

specification/network/resource-manager/Microsoft.Network/stable/2021-08-01/networkSecurityGroup.json

@@ -870,6 +870,10 @@
     },
     "NetworkSecurityGroupPropertiesFormat": {
       "properties": {
+        "flushConnection": {
+          "type": "boolean",
+          "description": "When enabled, flows created from Network Security Group connections will be re-evaluated when rules are updates. Initial enablement will trigger re-evaluation."
+        },
         "securityRules": {
           "type": "array",
           "items": {