### 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_
return "-".join([part.capitalize() for part in header_name.split("-")])
def get_kms_key_arn(kms_key: str, account_id: str, bucket_region: str) -> Optional[str]:
    """
    In S3, the KMS key can be passed as a KeyId or a KeyArn. This method allows to always get the KeyArn from either.
    It can also validate if the key is in the same region, and raise an exception.
    :param kms_key: the KMS key id or ARN
    :param account_id: the bucket account id
    :param bucket_region: the bucket region
    :raise KMS.NotFoundException if the key is not in the same region
    :return: the key ARN if found and enabled
    """
    if not kms_key:
        return None
    try:
        parsed_arn = parse_arn(kms_key)
        key_region = parsed_arn["region"]
        
        if bucket_region and key_region != bucket_region:
            raise CommonServiceException(
                code="KMS.NotFoundException", message=f"Invalid arn {key_region}"
            )
    except InvalidArnException:
        
        key_id = kms_key
        
        
        kms_key = arns.kms_key_arn(key_id=key_id, account_id=account_id, region_name=bucket_region)
    return kms_key
def validate_kms_key_id(kms_key: str, bucket: Any) -> None: