### 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_
topic_arn = sns_create_topic()["TopicArn"]
        # s
        message = "This is a test message" * 12000
        with pytest.raises(ClientError) as e:
            aws_client.sns.publish(TopicArn=topic_arn, Message=message)
        snapshot.match("error", e.value.response)
        assert e.value.response["Error"]["Code"] == "InvalidParameter"
        assert e.value.response["Error"]["Message"] == "Invalid parameter: Message too long"
        assert e.value.response["ResponseMetadata"]["HTTPStatusCode"] == 400
    @pytest.mark.only_localstack  # n
    @pytest.mark.xfail(reason="Need to implement credentials validation when creating platform")
    def test_publish_to_gcm(self, sns_create_platform_application, aws_client):
        key = "mock_server_key"
        token = "mock_token"
        response = sns_create_platform_application(
            Name="firebase", Platform="GCM", Attributes={"PlatformCredential": key}
        )
        platform_app_arn = response["PlatformApplicationArn"]
        response = aws_client.sns.create_platform_endpoint(
            PlatformApplicationArn=platform_app_arn,
            Token=token,
        )
        endpoint_arn = response["EndpointArn"]
        message = {
            "GCM": '{ "notification": {"title": "Title of notification", "body": "It works" } }'
        }