### 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_
aws_client.s3.put_bucket_inventory_configuration(
                Bucket=src_bucket,
                Id=config_id,
                InventoryConfiguration=inventory_configuration,
            )
        # put 
        with pytest.raises(ClientError) as e:
            inv_config = _get_config()
            inv_config["Id"] = config_id + "wrong"
            _put_bucket_inventory_configuration(inv_config)
        snapshot.match("wrong-id", e.value.response)
        # set 
        with pytest.raises(ClientError) as e:
            inv_config = _get_config()
            inv_config["Destination"]["S3BucketDestination"]["Bucket"] = dest_bucket
            _put_bucket_inventory_configuration(inv_config)
        snapshot.match("wrong-destination-arn", e.value.response)
        # set 
        with pytest.raises(ClientError) as e:
            inv_config = _get_config()
            inv_config["Destination"]["S3BucketDestination"]["Format"] = "WRONG-FORMAT"
            _put_bucket_inventory_configuration(inv_config)