### 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_
# Boto 
        # aws_
        # Test 
        _key = "test-runtime.properties"
        _data = (
            "#20211122+0100\n"
            "#Mon Nov 22 20:10:44 CET 2021\n"
            "last.sync.url.test-space-key=2822a50f-4992-425a-b8fb-923735a9ddff317e3479-5907-46cf-b33a-60da9709274f\n"
        )
        _data_chunked = (
            "93;chunk-signature=5be6b2d473e96bb9f297444da60bdf0ff8f5d2e211e1d551b3cf3646c0946641\r\n"
            f"{_data}"
            "\r\n0;chunk-signature=bd5c830b94346b57ddc8805ba26c44a122256c207014433bf6579b0985f21df7\r\n\r\n"
        )
        content_md5 = base64.b64encode(hashlib.md5(_data.encode()).digest()).decode()
        headers = {