### 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_
self, s3_create_bucket_with_client, patch_s3_skip_signature_validation_false, aws_client
    ):
        bucket_name = f"bucket-{short_uid()}"
        key_name = "key"
        response = aws_client.sts.get_session_token()
        if not is_aws_cloud():
            # Moto 
            # retr
            # we n
            response["Credentials"][
                "SecretAccessKey"
            ] = s3_constants.DEFAULT_PRE_SIGNED_SECRET_ACCESS_KEY
        client = boto3.client(
            "s3",
            config=Config(signature_version="s3v4"),
            endpoint_url=_endpoint_url(),
            aws_access_key_id=response["Credentials"]["AccessKeyId"],
            aws_secret_access_key=response["Credentials"]["SecretAccessKey"],
            aws_session_token=response["Credentials"]["SessionToken"],
        )
        s3_create_bucket_with_client(s3_client=client, Bucket=bucket_name)
        client.put_(Body="test-value", Bucket=bucket_name, Key=key_name)
        presigned_url = client.generate_presigned_url(
            ClientMethod="get_",
            Params={"Bucket": bucket_name, "Key": key_name},
            ExpiresIn=600,
        )
        response = .get(presigned_url)
        assert response._content == b"test-value"
    @pytest.mark.skipif(condition=TEST_S3_IMAGE, reason="STS not enabled in S3 image")