### 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_
kms_client = connect_to(aws_access_key_id=account_id, region_name=region_name).kms
    key = kms_client.create_key(
        Description="Default key that protects my S3 objects when no other key is defined"
    )
    return key["KeyMetadata"]["Arn"]
def rfc_1123_datetime(src: datetime.datetime) -> str:
    return src.strftime(RFC1123)
def str_to_rfc_1123_datetime(value: str) -> datetime.datetime:
    return datetime.datetime.strptime(value, RFC1123).replace(tzinfo=_gmt_zone_info)
def add_expiration_days_to_datetime(user_datatime: datetime.datetime, exp_days: int) -> str:
    """
    This adds expiration days to a datetime, rounding to the next day at midnight UTC.
    :param user_datatime: datetime object
    :param exp_days: provided days
    :return: return a datetime object, rounded to midnight, in string formatted to rfc_1123
    """
    rounded_datetime = user_datatime.replace(
        hour=0, minute=0, second=0, microsecond=0
    ) + datetime.timedelta(days=exp_days + 1)
    return rfc_1123_datetime(rounded_datetime)
def serialize_expiration_header(
    rule_id: str, lifecycle_exp: LifecycleExpiration, last_modified: datetime.datetime
):
    if exp_days := lifecycle_exp.get("Days"):
        
        exp_date = add_expiration_days_to_datetime(last_modified, exp_days)
    else:
        exp_date = rfc_1123_datetime(lifecycle_exp["Date"])
    return f'expiry-date="{exp_date}", rule-id="{rule_id}"'
def get_lifecycle_rule_from_object(