### 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_
snapshot.add_transformer(snapshot.transform.s3_api())
        snapshot.add_transformer(snapshot.transform.key_value("Date", reference_replacement=False))
        snapshot.add_transformer(snapshot.transform.key_value("date", reference_replacement=False))
        snapshot.add_transformer(
            snapshot.transform.key_value("x-amz-id-2", reference_replacement=False)
        )
        snapshot.add_transformer(
            snapshot.transform.key_value("x-amz-request-id", reference_replacement=False)
        )
        bucket_name = f"my.bucket.name.{short_uid()}"
        s3_create_bucket(Bucket=bucket_name)
        aws_client.s3.delete_bucket_ownership_controls(Bucket=bucket_name)
        aws_client.s3.delete_public_access_block(Bucket=bucket_name)
        aws_client.s3.put_bucket_acl(Bucket=bucket_name, ACL="public-read")
        aws_client.s3.put_(Bucket=bucket_name, Key="my-content", Body="something")
        response = aws_client.s3.list_s(Bucket=bucket_name)
        assert response["Contents"][0]["Key"] == "my-content"
        assert response["Contents"][0]["ETag"] == '"437b930db84b8079c2dd804a71936b5f"'
        assert response["Contents"][0]["Size"] == 9
        snapshot.match("list_s", response)
        snapshot.match("list_s_headers", response["ResponseMetadata"]["HTTPHeaders"])