### 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,
        aws_client_factory,
        s3_create_bucket_with_client,
        kms_create_key,
        monkeypatch,
        snapshot,
        aws_client,
    ):
        snapshot.add_transformer(snapshot.transform.key_value("Description"))
        data = b"test-sse"
        bucket_name = f"bucket-test-kms-{short_uid()}"
        region_1 = "us-east-2"
        snapshot.add_transformer(RegexTransformer(region_1, "<region_1>"))
        client = aws_client_factory(region_name=region_1).s3
        s3_create_bucket_with_client(
            client, Bucket=bucket_name, CreateBucketConfiguration={"LocationConstraint": region_1}
        )
        # crea
        region_2 = "us-west-2"
        snapshot.add_transformer(RegexTransformer(region_2, "<region_2>"))
        kms_key = kms_create_key(region_name=region_2)