### 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_
# ACL 
        response = secondary_client.get_(Bucket=bucket_name, Key=key_name)
        assert response["Body"].read() == body1
        assert secondary_client.put_(Bucket=bucket_name, Key=key_name, Body=body2)
        # The 
        response = primary_client.get_(Bucket=bucket_name, Key=key_name)
        assert response["Body"].read() == body2
    @markers.aws.unknown
    def test_cross_account_copy_(
        self, primary_client, secondary_client, cleanups, s3_empty_bucket
    ):
        bucket_name = short_uid()
        key_name = "lorem/ipsum"
        key_name_copy = "lorem/ipsum2"
        body1 = b"zaphod beeblebrox"
        # Firs
        create_s3_bucket(bucket_name=bucket_name, s3_client=primary_client)
        cleanups.append(lambda: primary_client.delete_bucket(Bucket=bucket_name))
        cleanups.append(lambda: s3_empty_bucket(bucket_name))
        primary_client.put_(Bucket=bucket_name, Key=key_name, Body=body1)
        # Asse
        response = secondary_client.copy_(
            Bucket=bucket_name, Key=key_name_copy, CopySource=f"{bucket_name}/{key_name}"
        )
        # Yet 
        response = secondary_client.list_s(Bucket=bucket_name)
        bucket_keys = {key["Key"] for key in response["Contents"]}
        assert key_name in bucket_keys
        assert key_name_copy in bucket_keys
class TestS3TerraformRawRequests: