[request]: Implement paginator for DescribeRules in aws-sdk-elasticloadbalancingv2

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### Community Note
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### Tell us about your request

Paginator for `DescribeRules` in aws-sdk-elasticloadbalancingv2.

### Tell us about the problem you're trying to solve.

I want to describe all rules for a listener by listener's ARN. `DescribeRules` operation has an interface for pagination (`marker`, `next_marker`, etc.) and I have to use them to list up all rules for a listener. Some operations in aws-sdk-elasticloadbalancingv2 has paginator implementations so they can be paginated easily, but `DescribeRules` does not. Having paginator for `DescribeRules` would be nice.

### Are you currently working around this issue?

Implements pagination manually. Note that the following code is for v0.3.0.

```rust
client
.describe_rules()
.listener_arn(listener_arn.clone())
.send()
.and_then(move |output| async move {
let next_marker = output.next_marker.clone();
let head = futures::stream::once(async { Ok(output) });
let tail = futures::stream::try_unfold(next_marker, move |next_marker| {
let listener_arn = listener_arn.clone();
async move {
let next_marker = match next_marker {
Some(marker) if !marker.is_empty() => marker,
_ => return Ok(None),
};

let output = elbv2
.describe_rules()
.marker(next_marker)
.listener_arn(listener_arn.clone())
.send()
.await?;
let next_marker = output.next_marker.clone();
Ok(Some((output, next_marker)))
}
});
Ok(head.chain(tail))
})
.try_flatten_stream()
```

### Additional context

_No response_

Start by comparing the existing paginator implementations in aws-sdk-elasticloadbalancingv2 with the DescribeRules operation and its marker and next_marker fields. Done means DescribeRules can paginate rules for a listener ARN without the manual stream workaround shown in the issue; verify behavior using the repository's existing paginator tests or patterns.

Written by the indexing model from the issue text.