### 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_
"""Register the platform endpointmessages retrospection endpoint as an internal LocalStack endpoint."""
    router.add(SNSServicePlatformEndpointMessagesApiResource())
def _format_platform_endpoint_messages(sent_messages: List[Dict[str, str]]):
    """
    This method format the messages to be more readable and undo the format change that was needed for Moto
    Should be removed once we refactor SNS.
    """
    validated_keys = [
        "TargetArn",
        "TopicArn",
        "Message",
        "MessageAttributes",
        "MessageStructure",
        "Subject",
        "MessageId",
    ]
    formatted_messages = []
    for sent_message in sent_messages:
        msg = {
            key: value if key != "Message" else json.dumps(value)
            for key, value in sent_message.items()
            if key in validated_keys
        }
        formatted_messages.append(msg)
    return formatted_messages
class SNSServicePlatformEndpointMessagesApiResource: