### 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_
with pytest.raises(queue.Empty):
                # m
                _requests.get(timeout=1)
            # a
            sub_1 = subscription_list["Subscriptions"][0]
            sub_1_attrs = aws_client.sns.get_subscription_attributes(
                SubscriptionArn=sub_1["SubscriptionArn"]
            )
            assert sub_1_attrs["Attributes"]["PendingConfirmation"] == "true"
            # a
            sub_2 = subscription_list["Subscriptions"][1]
            sub_2_attrs = aws_client.sns.get_subscription_attributes(
                SubscriptionArn=sub_2["SubscriptionArn"]
            )
            assert sub_2_attrs["Attributes"]["PendingConfirmation"] == "true"
            # c
            response = aws_client.sns.confirm_subscription(TopicArn=topic_arn, Token=tokens[0])
            # a
            assert response["SubscriptionArn"] == sub_1["SubscriptionArn"]
            # a
            sub_1_attrs = aws_client.sns.get_subscription_attributes(
                SubscriptionArn=sub_1["SubscriptionArn"]
            )
            assert sub_1_attrs["Attributes"]["PendingConfirmation"] == "false"
            # a
            sub_2_attrs = aws_client.sns.get_subscription_attributes(
                SubscriptionArn=sub_2["SubscriptionArn"]
            )
            assert sub_2_attrs["Attributes"]["PendingConfirmation"] == "true"
        finally: