### 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_
"""
    if hasattr(bucket, "region_name"):
        bucket_region = bucket.region_name
    else:
        bucket_region = bucket.bucket_region
    if hasattr(bucket, "account_id"):
        bucket_account_id = bucket.account_id
    else:
        bucket_account_id = bucket.bucket_account_id
    kms_key_arn = get_kms_key_arn(kms_key, bucket_account_id, bucket_region)
    
    kms_client = connect_to(region_name=bucket_region).kms
    try:
        key = kms_client.describe_key(KeyId=kms_key_arn)
        if not key["KeyMetadata"]["Enabled"]:
            if key["KeyMetadata"]["KeyState"] == "PendingDeletion":
                raise CommonServiceException(
                    code="KMS.KMSInvalidStateException",
                    message=f'{key["KeyMetadata"]["Arn"]} is pending deletion.',
                )
            raise CommonServiceException(
                code="KMS.DisabledException", message=f'{key["KeyMetadata"]["Arn"]} is disabled.'
            )
    except ClientError as e:
        if e.response["Error"]["Code"] == "NotFoundException":
            raise CommonServiceException(
                code="KMS.NotFoundException", message=e.response["Error"]["Message"]
            )
        raise
def create_s3_kms_managed_key_for_region(account_id: str, region_name: str) -> SSEKMSKeyId: