### 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_
return aws_client_factory.get_client(
            service_name=service_name,
            region_name=region_name,
            aws_access_key_id=SECONDARY_TEST_AWS_ACCESS_KEY_ID,
            aws_secret_access_key=SECONDARY_TEST_AWS_SECRET_ACCESS_KEY,
            config=Config(signature_version=UNSIGNED),
        )
    yield _anonymous_client
@pytest.fixture(scope="function")
def patch_s3_skip_signature_validation_false(monkeypatch):
    monkeypatch.setattr(config, "S3_SKIP_SIGNATURE_VALIDATION", False)
@pytest.fixture
def s3_create_bucket_with_client(s3_empty_bucket, aws_client):
    buckets = []
    def factory(s3_client, **kwargs) -> str:
        if "Bucket" not in kwargs:
            kwargs["Bucket"] = f"test-bucket-{short_uid()}"
        response = s3_client.create_bucket(**kwargs)
        buckets.append(kwargs["Bucket"])
        return response
    yield factory
    
    for bucket in buckets:
        try:
            s3_empty_bucket(bucket)
            aws_client.s3.delete_bucket(Bucket=bucket)
        except Exception as e:
            LOG.debug(f"error cleaning up bucket {bucket}: {e}")
@pytest.fixture
def s3_multipart_upload(aws_client):