### 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_
start = int(time.time() + 100) << 33
    
    return itertools.count(start)
def get_next_sequence_number():
    return next(global_sns_message_sequence())
@dataclass
class SnsMessage:
    type: str
    message: Union[
        str, Dict
    ]  
    message_attributes: Optional[MessageAttributeMap] = None
    message_structure: Optional[str] = None
    subject: Optional[str] = None
    message_deduplication_id: Optional[str] = None
    message_group_id: Optional[str] = None
    token: Optional[str] = None
    message_id: str = field(default_factory=long_uid)
    is_fifo: Optional[bool] = False
    sequencer_number: Optional[str] = None
    def __post_init__(self):