fix(iam): allow intrinsic functions in deletion policy (#28834)

> # Issue
> > When using `CfnInclude` it was not possible to have an intrinsic function in the `DeletionPolicy`. It only allowed the DeletionPolicy to be explicitly defined. 
> # Solution
> > Check if policy looks like an intrinsic. Check if it is an explicitly defined DeletionPolicy. Then Default to a case that checks if this is an intrinsic if it is return the policy after using parseValue. Else throw the same error it was previously.
> # Important Design Decisions
> > Unsure if any have been made please let me know if there are any I didn't think were Important Design Decisions. 
>
> Remember to follow the [CONTRIBUTING GUIDE] and [DESIGN GUIDELINES] for any
> code you submit.
>
> [CONTRIBUTING GUIDE]: https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md
> [DESIGN GUIDELINES]: https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md

Closes #28292 .

----

*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/cloudformation-include/test/integ.intrinsic-deletion-policy.js.snapshot/Stack.template.json

@@ -0,0 +1,58 @@
+{
+ "Conditions": {
+  "AlwaysFalseCond": {
+   "Fn::Equals": [
+    {
+     "Ref": "AWS::Region"
+    },
+    "completely-made-up-region"
+   ]
+  }
+ },
+ "Resources": {
+  "Bucket": {
+   "Type": "AWS::S3::Bucket",
+   "DeletionPolicy": {
+    "Fn::If": [
+     "AlwaysFalseCond",
+     "Retain",
+     "Delete"
+    ]
+   }
+  }
+ },
+ "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."
+    }
+   ]
+  }
+ }
+}