### 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_
url = f"{website_url}/actual/key.html"
        response = .get(url, verify=False)
        assert response.status_code == 200
        assert response.text == "key"
        assert "content-type" in response.headers
        assert response.headers["content-type"] == "text/html"
        assert "etag" in response.headers
        assert actual_key_obj["ETag"] in response.headers["etag"]
        # If-N
        response = .get(
            url, headers={"If-None-Match": actual_key_obj["ETag"]}, verify=False
        )
        assert response.status_code == 304
        # key 
        url = f"{website_url}/with-content-type/key.js"
        response = .get(url, verify=False)
        assert response.status_code == 200
        assert response.text == "some js"
        assert "content-type" in response.headers
        assert response.headers["content-type"] == "application/javascript; charset=utf-8"
        assert "etag" in response.headers
        assert response.headers["etag"] == with_content_type_obj["ETag"]
        # inde
        url = f"{website_url}/test"
        response = .get(url, verify=False)
        assert response.status_code == 200
        assert response.text == "index"
        assert "content-type" in response.headers
        assert "text/html" in response.headers["content-type"]
        assert "etag" in response.headers