feat(appconfig): add grantReadConfig method to Environment Construct (#30180)

### Issue # (if applicable)

Closes #28585

### Reason for this change
To simplify policy configuration for AppConfig Environments.



### Description of changes
add grantReadConfig method to Environment Construct



### Description of how you validated changes
Add unit test and integ tests


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: mazyu36

packages/@aws-cdk-testing/framework-integ/test/aws-appconfig/test/integ.environment-grant.js.snapshot/appconfigenvironmentDefaultTestDeployAssert75BD28E7.assets.json

@@ -0,0 +1,107 @@
+{
+ "Resources": {
+  "MyApplicationForEnv1F597ED9": {
+   "Type": "AWS::AppConfig::Application",
+   "Properties": {
+    "Name": "AppForEnvTest"
+   }
+  },
+  "MyEnvironment465E4DEA": {
+   "Type": "AWS::AppConfig::Environment",
+   "Properties": {
+    "ApplicationId": {
+     "Ref": "MyApplicationForEnv1F597ED9"
+    },
+    "Name": "awsappconfigenvironmentgrant-MyEnvironment-6CC47125"
+   }
+  },
+  "MyUserDC45028B": {
+   "Type": "AWS::IAM::User"
+  },
+  "MyUserDefaultPolicy7B897426": {
+   "Type": "AWS::IAM::Policy",
+   "Properties": {
+    "PolicyDocument": {
+     "Statement": [
+      {
+       "Action": [
+        "appconfig:GetLatestConfiguration",
+        "appconfig:StartConfigurationSession"
+       ],
+       "Effect": "Allow",
+       "Resource": {
+        "Fn::Join": [
+         "",
+         [
+          "arn:",
+          {
+           "Ref": "AWS::Partition"
+          },
+          ":appconfig:",
+          {
+           "Ref": "AWS::Region"
+          },
+          ":",
+          {
+           "Ref": "AWS::AccountId"
+          },
+          ":application/",
+          {
+           "Ref": "MyApplicationForEnv1F597ED9"
+          },
+          "/environment/",
+          {
+           "Ref": "MyEnvironment465E4DEA"
+          },
+          "/configuration/*"
+         ]
+        ]
+       }
+      }
+     ],
+     "Version": "2012-10-17"
+    },
+    "PolicyName": "MyUserDefaultPolicy7B897426",
+    "Users": [
+     {
+      "Ref": "MyUserDC45028B"
+     }
+    ]
+   }
+  }
+ },
+ "Parameters": {
+  "BootstrapVersion": {
+   "Type": "AWS::SSM::Parameter::Value<String>",
+   "Default": "/cdk-bootstrap/hnb659fds/version",
+   "Description": "Version of the CDK Bootstrap resources in this environment, automatically retrieved from SSM Parameter Store. [cdk:skip]"
+  }
+ },
+ "Rules": {
+  "CheckBootstrapVersion": {
+   "Assertions": [
+    {
+     "Assert": {
+      "Fn::Not": [
+       {
+        "Fn::Contains": [
+         [
+          "1",
+          "2",
+          "3",
+          "4",
+          "5"
+         ],
+         {
+          "Ref": "BootstrapVersion"
+         }
+        ]
+       }
+      ]
+     },
+     "AssertDescription": "CDK bootstrap stack version 6 required. Please run 'cdk bootstrap' with a recent version of the CDK CLI."
+    }
+   ]
+  }
+ }
+}