### 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_
assert (
            api_platform_endpoints_msgs[endpoint_arn][0]["MessageAttributes"] == message_attributes
        )
        # E
        msg_with_region = requests.get(msgs_url, params={"region": "eu-west-1"}).json()
        assert len(msg_with_region["platform_endpoint_messages"]) == 0
        assert msg_with_region["region"] == "eu-west-1"
        # E
        api_contents_with_endpoint = requests.get(
            msgs_url, params={"endpointArn": endpoint_arn}
        ).json()
        msgs_with_endpoint = api_contents_with_endpoint["platform_endpoint_messages"]
        assert len(msgs_with_endpoint) == 1
        assert len(msgs_with_endpoint[endpoint_arn]) == 1
        assert api_contents_with_endpoint["region"] == "us-east-1"
        # E
        delete_res = requests.delete(msgs_url, params={"endpointArn": endpoint_arn})
        assert delete_res.status_code == 204
        api_contents_with_endpoint = requests.get(
            msgs_url, params={"endpointArn": endpoint_arn}
        ).json()
        msgs_with_endpoint = api_contents_with_endpoint["platform_endpoint_messages"]
        assert len(msgs_with_endpoint[endpoint_arn]) == 0
        # E
        delete_res = requests.delete(msgs_url, params={"region": "us-east-1"})
        assert delete_res.status_code == 204
        msg_with_region = requests.get(msgs_url, params={"region": "us-east-1"}).json()
        assert not msg_with_region["platform_endpoint_messages"]
    @pytest.mark.only_localstack
    def test_publish_to_platform_endpoint_is_dispatched(