### 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: BucketName, object_key: ObjectKey, version_id: ObjectVersionId
) -> str:
    return f"{bucket}/{object_key}/{version_id or 'null'}"
def get_retention_from_now(days: int = None, years: int = None) -> datetime.datetime:
    """
    This calculates a retention date from now, adding days or years to it
    :param days: provided days
    :param years: provided years, exclusive with days
    :return: return a datetime object
    """
    if not days and not years:
        raise ValueError("Either 'days' or 'years' needs to be provided")
    now = datetime.datetime.now(tz=_gmt_zone_info)
    if days:
        retention = now + datetime.timedelta(days=days)
    else:
        retention = now.replace(year=now.year + years)
    return retention
def get_failed_precondition_copy_source(