### 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 re
from string import ascii_letters, digits
SNS_PROTOCOLS = [
    "http",
    "https",
    "email",
    "email-json",
    "sms",
    "sqs",
    "application",
    "lambda",
    "firehose",
]
VALID_SUBSCRIPTION_ATTR_NAME = [
    "DeliveryPolicy",
    "FilterPolicy",
    "FilterPolicyScope",
    "RawMessageDelivery",
    "RedrivePolicy",
    "SubscriptionRoleArn",
]
MSG_ATTR_NAME_REGEX = re.compile(r"^(?!\.)(?!.*\.$)(?!.*\.\.)[a-zA-Z0-9_\-.]+$")
ATTR_TYPE_REGEX = re.compile(r"^(String|Number|Binary)\..+$")
VALID_MSG_ATTR_NAME_CHARS = set(ascii_letters + digits + "." + "-" + "_")
GCM_URL = "https://fcm.googleapis.com/fcm/send"
PLATFORM_ENDPOINT_MSGS_ENDPOINT = "/_aws/sns/platform-endpoint-messages"