feat(kms): add multiRegion property to a Key (#31125)

### Issue # (if applicable)

None

### Reason for this change

We can create a multi-Region primary key for a KMS key from cloudformation, but this was not supported in the AWS CDK L2 construct.

### Description of changes

Add multiRegion property to KeyProps and set it in the CfnKey constructor.

### Description of how you validated changes

Added both unit and integration 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*

packages/@aws-cdk-testing/framework-integ/test/aws-kms/test/integ.key-multi-region.js.snapshot/KmsKeyMultiRegionStack.template.json

@@ -0,0 +1,74 @@
+{
+ "Resources": {
+  "keyFEDD6EC0": {
+   "Type": "AWS::KMS::Key",
+   "Properties": {
+    "KeyPolicy": {
+     "Statement": [
+      {
+       "Action": "kms:*",
+       "Effect": "Allow",
+       "Principal": {
+        "AWS": {
+         "Fn::Join": [
+          "",
+          [
+           "arn:",
+           {
+            "Ref": "AWS::Partition"
+           },
+           ":iam::",
+           {
+            "Ref": "AWS::AccountId"
+           },
+           ":root"
+          ]
+         ]
+        }
+       },
+       "Resource": "*"
+      }
+     ],
+     "Version": "2012-10-17"
+    },
+    "MultiRegion": true
+   },
+   "UpdateReplacePolicy": "Retain",
+   "DeletionPolicy": "Retain"
+  }
+ },
+ "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."
+    }
+   ]
+  }
+ }
+}