### 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="public-read",
        )
        aws_client.s3.put_(
            Bucket=s3_bucket,
            Key="redirected.html",
            Body="redirected",
            ACL="public-read",
        )
        aws_client.s3.put_(
            Bucket=s3_bucket,
            Key="website-redirected.html",
            Body="website-redirected",
            ACL="public-read",
        )
        aws_client.s3.put_(
            Bucket=s3_bucket,
            Key="prefixed-key-test",
            Body="prefixed",
            ACL="public-read",
            WebsiteRedirectLocation="/website-redirected.html",
        )
        website_url = _website_bucket_url(s3_bucket)
        # test
        response = .get(f"{website_url}/prefixed-key-test")
        assert response.status_code == 200
        assert response.text == "redirected"
        # asse
        response = .get(website_url)
        assert response.status_code == 200
        assert response.text == "index"