feat(kms): allow fromLookup method to return dummy key if target key was not found (#31676)

### Issue # (if applicable)

Closes #31574.

### Reason for this change



The `fromLookup` method causes an error if the target key was not found. However it would be also good not to cause an error in that case. 

### Description of changes



Added `returnDummyKeyOnMissing` in `KeyLookupOptions`. If the property is set to true, the context method will not cause an error and will return a dummy key if the key was not found.

Originally, I thought to make the method to return undefined in that case, but the return type of method is `IKey`. If we change the type to `IKey | undefined`, it should be a breaking change.

```ts
  public static fromLookup(scope: Construct, id: string, options: KeyLookupOptions): IKey {
```

So I decided to return a dummy key with a dummy key id '1234abcd-12ab-34cd-56ef-1234567890ab'. The dummy key id had been defined originally (see: https://github.com/aws/aws-cdk/blob/v2.161.0/packages/aws-cdk-lib/aws-kms/lib/key.ts#L686).

The property `returnDummyKeyOnMissing` will be passed to `ignoreErrorOnMissingContext` added in the [PR](#31415). If the `ignoreErrorOnMissingContext` is true and the key doesn't exist, an error will be suppressed in the `ContextProvider`.

### Additional information

see: #31574 (comment)

### Description of how you validated changes



Both of unit 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: go-to-k

packages/@aws-cdk-testing/framework-integ/test/aws-kms/test/integ.key-from-lookup-dummy.js.snapshot/cdk.out

@@ -0,0 +1,41 @@
+{
+ "Outputs": {
+  "KeyId": {
+   "Value": "1234abcd-12ab-34cd-56ef-1234567890ab"
+  }
+ },
+ "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."
+    }
+   ]
+  }
+ }
+}