### 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_
bucket_name = bucket_name or ""
    bucket_name = bucket_name.lower()
    return bucket_name
def get_bucket_and_key_from_s3_uri(s3_uri: str) -> Tuple[str, str]:
    """
    Extracts the bucket name and key from s3 uri
    """
    output_bucket, _, output_key = s3_uri.removeprefix("s3://").partition("/")
    return output_bucket, output_key
def get_bucket_and_key_from_presign_url(presign_url: str) -> Tuple[str, str]:
    """
    Extracts the bucket name and key from s3 presign url
    """
    parsed_url = urlparser.urlparse(presign_url)
    bucket = parsed_url.path.split("/")[1]
    key = "/".join(parsed_url.path.split("/")[2:]).split("?")[0]
    return bucket, key
def _create_invalid_argument_exc(
    message: Union[str, None], name: str, value: str, host_id: str = None
) -> InvalidArgument:
    ex = InvalidArgument(message)
    ex.ArgumentName = name
    ex.ArgumentValue = value
    if host_id:
        ex.HostId = host_id
    return ex
def capitalize_header_name_from_snake_case(header_name: str) -> str: