### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

SNS allows for the publishing of messages to an SMS destination with a phone number. Those messages are logged and stored in the `SnsStore`, but there is no way to retrieve them for verification. The request here is to expose a new endpoint which returns SMS messages from the store, similar to the one made available to retrieve email messages sent via SES.

### 🧑‍💻 Implementation

The `SNSServicePlatformEndpointMessagesApiResource` class makes endpoints available for accessing platform endpoint messages sent via SNS. A similar resource class could be implemented to provide new endpoints for accessing SMS messages.

Given that interaction platform endpoint messages is exposed at the path `/_aws/sns/platform-endpoint-messages`, SMS message interaction would presumably be exposed at `/_aws/sns/sms-messages`. A `GET` endpoint could accept an optional `phoneNumber` query parameter to filter messages based on the destination phone number.

```python
class SNSServiceSMSMessagesApiResource:
  @route(sns_constants.SMS_MSGS_ENDPOINT, methods=["GET"])
    def on_get(self, request: Request):
      account_id = #...
      region = #...
      filter_phone_number = request.args.get("phoneNumber")
      # get store; conditionally filter messages based on filter_phone_number
```

### Anything else?

_No response_
message_ctx = SnsMessage(
            type="Notification",
            message=message,
            message_attributes=message_attributes,
            message_deduplication_id=message_deduplication_id,
            message_group_id=message_group_id,
            message_structure=message_structure,
            subject=subject,
            is_fifo=is_fifo,
        )
        publish_ctx = SnsPublishContext(
            message=message_ctx, store=store, request_headers=context.request.headers
        )
        if is_endpoint_publish:
            self._publisher.publish_to_application_endpoint(
                ctx=publish_ctx, endpoint_arn=target_arn
            )
        elif phone_number:
            self._publisher.publish_to_phone_number(ctx=publish_ctx, phone_number=phone_number)
        else:
            
            
            
            self._publisher.publish_to_topic(publish_ctx, topic_or_target_arn)
        if is_fifo:
            return PublishResponse(
                MessageId=message_ctx.message_id, SequenceNumber=message_ctx.sequencer_number
            )
        return PublishResponse(MessageId=message_ctx.message_id)
    def subscribe(