### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
if not region:
        region = AWS_REGION_US_EAST_1
    if is_aws_cloud():
        if region == "us-east-1":
            return f"https://{bucket_name}.s3.amazonaws.com"
        else:
            return f"https://{bucket_name}.s3.{region}.amazonaws.com"
    host_definition = get_localstack_host()
    if localstack_host:
        host_and_port = f"{localstack_host}:{config.GATEWAY_LISTEN[0].port}"
    else:
        host_and_port = (
            f"s3.{region}.{host_definition.host_and_port()}"
            if region != "us-east-1"
            else f"s3.{host_definition.host_and_port()}"
        )
    # TODO might add the region here
    return f"{config.get_protocol()}://{bucket_name}.{host_and_port}"
def _generate_presigned_url(
    client: "S3Client", params: dict, expires: int, client_method: str = "get_"
) -> str:
    return client.generate_presigned_url(
        client_method,
        Params=params,
        ExpiresIn=expires,
    )
def _make_url_invalid(url_prefix: str, _key: str, url: str) -> str: