### 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_
class TestSNSDelivery:
    @pytest.mark.aws_validated
    @pytest.mark.skip_snapshot_verify(
        paths=[
            "$.get-topic-attrs.Attributes.DeliveryPolicy",
            "$.get-topic-attrs.Attributes.EffectiveDeliveryPolicy",
            "$.get-topic-attrs.Attributes.Policy.Statement..Action",  # S
        ]
    )
    def test_delivery_lambda(
        self,
        sns_create_topic,
        sns_subscription,
        lambda_su_role,
        create_lambda_function,
        create_role,
        create_policy,
        snapshot,
        aws_client,
    ):
        snapshot.add_transformers_list(
            [
                snapshot.transform.key_value(
                    "dwellTimeMs", reference_replacement=False, value_replacement="<time-ms>"
                ),
                snapshot.transform.key_value("nextBackwardToken"),
                snapshot.transform.key_value("nextForwardToken"),
            ]
        )
        function_name = f"lambda-function-{short_uid()}"