### 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_
key = f"Checksum{checksum_algorithm.upper()}"
    
    checksum = request.get(key)
    calculated_checksum = get_object_checksum_for_algorithm(checksum_algorithm, data)
    if calculated_checksum != checksum:
        raise InvalidRequest(
            f"Value for x-amz-checksum-{checksum_algorithm.lower()} header is invalid."
        )
def etag_to_base_64_content_md5(etag: ETag) -> str:
    """
    Convert an ETag, representing an md5 hexdigest (might be quoted), to its base64 encoded representation
    :param etag: an ETag, might be quoted
    :return: the base64 value
    """
    
    byte_digest = codecs.decode(to_bytes(etag.strip('"')), "hex")
    return to_str(base64.b64encode(byte_digest))
def decode_aws_chunked_object(