[in_app_purchase_storekit]add storekit configuration to the example app (#5411)

Adds the storekit test config to the example app so the example app runs with the config file by default.
This will allow adding XCUITests to the plugin. 

part of https://github.com/flutter/flutter/issues/138516

packages/in_app_purchase/in_app_purchase_storekit/example/ios/Runner.xcodeproj/project.pbxproj

@@ -257,7 +257,7 @@
 			isa = PBXProject;
 			attributes = {
 				DefaultBuildSystemTypeForWorkspace = Original;
-				LastUpgradeCheck = 1300;
+				LastUpgradeCheck = 1430;
 				ORGANIZATIONNAME = "The Flutter Authors";
 				TargetAttributes = {
 					97C146ED1CF9000F007C117D = {

packages/in_app_purchase/in_app_purchase_storekit/example/ios/Runner.xcodeproj/xcshareddata/xcschemes/Runner.xcscheme

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1300"
+   LastUpgradeVersion = "1430"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"
@@ -69,6 +69,9 @@
             ReferencedContainer = "container:Runner.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
+      <StoreKitConfigurationFileReference
+         identifier = "../Runner/Configuration.storekit">
+      </StoreKitConfigurationFileReference>
    </LaunchAction>
    <ProfileAction
       buildConfiguration = "Release"

packages/in_app_purchase/in_app_purchase_storekit/example/ios/Runner/Configuration.storekit

@@ -36,7 +36,56 @@
     }
   ],
   "settings" : {
-
+    "_failTransactionsEnabled" : false,
+    "_locale" : "en_US",
+    "_storefront" : "USA",
+    "_storeKitErrors" : [
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Load Products"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Purchase"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Verification"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "App Store Sync"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Subscription Status"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "App Transaction"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Manage Subscriptions Sheet"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Refund Request Sheet"
+      },
+      {
+        "current" : null,
+        "enabled" : false,
+        "name" : "Offer Code Redeem Sheet"
+      }
+    ]
   },
   "subscriptionGroups" : [
     {
@@ -49,6 +98,9 @@
         {
           "adHocOffers" : [
 
+          ],
+          "codeOffers" : [
+
           ],
           "displayPrice" : "4.99",
           "familyShareable" : false,
@@ -71,6 +123,9 @@
         {
           "adHocOffers" : [
 
+          ],
+          "codeOffers" : [
+
           ],
           "displayPrice" : "5.99",
           "familyShareable" : false,
@@ -94,7 +149,7 @@
     }
   ],
   "version" : {
-    "major" : 1,
-    "minor" : 1
+    "major" : 3,
+    "minor" : 0
   }
 }