aws_sns: Add support for $or operator in subscription filter policies

### Describe the feature

https://docs.aws.amazon.com/sns/latest/dg/and-or-logic.html#or-operator

I would like to be able to use the "$or" operator for SNS subscription filters to filter out messages based on multiple combinations of message attributes.

### Use Case

I would like to create the following filter policy on an SNS subscription:

```json
{
"$or": [
{
"attribute_1": [
"value_1",
"value_2"
]
},
{
"attribute_1": [
"value_3"
],
"attribute_2": [
"value_4"
]
}
]
}
```

However, the `filter_policy` on an SNS subscription is a `Mapping[str, SubscriptionFilter]`, which doesn't account for the "$or" operator which effectively takes a list of filter policies. https://docs.aws.amazon.com/cdk/api/v2/python/aws_cdk.aws_sns/Subscription.html

I can get my desired result, but I have to set the filter policy directly:
```python
subscription = self._topic.add_subscription(
aws_sns_subscriptions.SqsSubscription(
self._queue,
)
)

subscription.node.default_child.filter_policy = filter_policy
```
where filter_policy is the dictionary at the beginning of the section.

I was unable to find if this was already supported in the documentation.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2.141.0

### Environment details (OS name and version, etc.)

MacOS, Python 3.9.6

Start at the aws_sns Subscription filter_policy entry point and compare it with SqsSubscription and the generated Python API referenced in the issue. Check the AWS SNS $or operator documentation, then verify that the public filter-policy type accepts the example and that the synthesized subscription policy preserves its structure.

Written by the indexing model from the issue text.