Update the label property of request body of find target resource api (Azure#17917)

* Update the label property of request body of find target resource api

It should be a map with the key of "label".

Right now the request body is defined as:
{
  "key":"value"
}

But it should be changed to:
{
  "labels":{
    "key":"value"
   }
}

* Update a description

* Fix validation check of example json file for find target resource group api

Author: peter-li-ms

specification/extendedlocation/resource-manager/Microsoft.ExtendedLocation/preview/2021-08-31-preview/customlocations.json

@@ -421,13 +421,13 @@
             "$ref": "#/parameters/ResourceNameParameter"
           },
           {
-            "name": "labels",
+            "name": "parameters",
             "in": "body",
             "required": true,
             "schema": {
               "$ref": "#/definitions/customLocationFindTargetResourceGroupProperties"
             },
-            "description": "Labels supplied to match with Resource Sync Rule. This is a map of {key,value} pairs."
+            "description": "Parameters of the find target resource group request."
           }
         ],
         "responses": {
@@ -878,10 +878,16 @@
       ]
     },
     "customLocationFindTargetResourceGroupProperties": {
-      "description": "Labels of the custom resource, this is a map of {key,value} pairs.",
+      "description": "The Find Target Resource Group operation request.",
       "type": "object",
-      "additionalProperties": {
-        "type": "string"
+      "properties": {
+        "labels": {
+          "description": "Labels of the custom resource, this is a map of {key,value} pairs.",
+          "type": "object",
+          "additionalProperties": {
+            "type": "string"
+          }
+        }
       }
     },
     "customLocationFindTargetResourceGroupResult": {

specification/extendedlocation/resource-manager/Microsoft.ExtendedLocation/preview/2021-08-31-preview/examples/CustomLocationsFindTargetResourceGroup.json

@@ -4,9 +4,11 @@
     "subscriptionId": "11111111-2222-3333-4444-555555555555",
     "resourceGroupName": "testresourcegroup",
     "resourceName": "customLocation01",
-    "labels": {
-      "key1": "value1",
-      "key2": "value2"
+    "parameters": {
+      "labels": {
+        "key1": "value1",
+        "key2": "value2"
+      }
     }
   },
   "responses": {