aws-lambda: Defining a `deadLetterQueue` or `deadLetterTopic` will *always* add a policy to the function's execution role

### Describe the bug

As indicated in the title, if you define a `deadLetterQueue` or `deadLetterTopic` on a `Function`, it will **always** append an inline policy to the execution role which is associated with the function.

I would suggest that this is expected behaviour if the `Function` creates the IAM role, but it may be unexpected if the IAM role is defined elsewhere. It feels a lot like a side-effect. This feels like a problem within the same CloudFormation stack, but would probably be even more unexpected if the IAM role being referenced originated outside the stack.

### Expected Behavior

I created an IAM role and SQS queue adjacent to a Lambda Function. I would have expected that if my IAM role were lacking a permission, it would:

* Ideally, throw an error due to a missing permission (although this may be hard to implement, especially for non-stack IAM roles); or
* Simply fail to drop failing events to the DLQ due to a lacking permission (this is less ideal because it may go unnoticed)

### Current Behavior

IAM policies for SQS permission will indiscriminately be added to IAM roles no matter where that role originates from

### Reproduction Steps

#### Relevant CDK Source Code

https://github.com/aws/aws-cdk/blob/5347369fa11f4f11ab3893b9ac4c8467c5d514c3/packages/aws-cdk-lib/aws-lambda/lib/function.ts#L1596-L1599

https://github.com/aws/aws-cdk/blob/5347369fa11f4f11ab3893b9ac4c8467c5d514c3/packages/aws-cdk-lib/aws-lambda/lib/function-base.ts#L375-L381

#### Partial Code to Reproduce Behaviour

```python
queue = aws_sqs.Queue(self, "queue")
role = aws_iam.Role(
self,
"role",
managed_policies=[
aws_iam.ManagedPolicy.from_aws_managed_policy_name(
"service-role/AWSLambdaVPCAccessExecutionRole"
),
],
assumed_by=aws_iam.ServicePrincipal("lambda.amazonaws.com"),
)
function = aws_lambda.Function(
...
role=role,
dead_letter_queue=queue,
...
)
```

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

2.114.1

### Framework Version

2.114.1

### Node.js Version

20.8.1

### OS

macOS 14.2.1

### Language

Python

### Language Version

3.11.6

### Other information

_No response_

Start by reading the referenced sections of packages/aws-cdk-lib/aws-lambda/lib/function.ts and function-base.ts, then synthesize the Python reproduction with an externally defined IAM role, SQS queue, and Lambda dead-letter queue. Done means the behavior for supplied roles and function-created roles is explicitly resolved without indiscriminately adding SQS permissions.

Written by the indexing model from the issue text.