### 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_
import contextlib
import json
import logging
import queue
import random
import time
from io import BytesIO
from operator import itemgetter
import pytest
import requests
import xmltodict
from botocore.exceptions import ClientError
from pytest_httpserver import HTTPServer
from werkzeug import Response
from localstack import config
from localstack.aws.accounts import get_aws_account_id
from localstack.aws.api.lambda_ import Runtime
from localstack.constants import TEST_AWS_ACCOUNT_ID, TEST_AWS_REGION_NAME
from localstack.services.sns.constants import PLATFORM_ENDPOINT_MSGS_ENDPOINT