Errors when updating the challenge template

Hi,

I am getting the following errors when I update the `challenge_config.yaml` after using the given template initially. I understand the reasons behind some of these checks but at the same time, it is quite confusing that one can't change things even during the challenge development phase. It seems like a hard-requirement for the host to update the template in one go on the `challenge` branch otherwise these errors would start to pop up.

```
Following errors occurred while validating the challenge config:
ERROR: Challenge phase 2 not found in config. Deletion of existing challenge phase after challenge creation is not allowed.
ERROR: Dataset split 3 doesn't exist. Addition of a new dataset split after challenge creation is not allowed.
ERROR: Challenge phase split (leaderboard_id: 1, challenge_phase_id: 1, dataset_split_id: 2) doesn't exist. Addition of challenge phase split after challenge creation is not allowed.
ERROR: Challenge phase split (leaderboard_id: 1, challenge_phase_id: 1, dataset_split_id: 3) doesn't exist. Addition of challenge phase split after challenge creation is not allowed.
ERROR: Challenge phase split (leaderboard_id: 1, challenge_phase_id: 2, dataset_split_id: 2) not found in config. Deletion of existing challenge phase split after challenge creation is not allowed.
ERROR: Challenge phase split (leaderboard_id: 1, challenge_phase_id: 2, dataset_split_id: 1) not found in config. Deletion of existing challenge phase split after challenge creation is not allowed.
There was an error while creating an issue: 404 {"message": "Not Found", "documentation_url": "https://docs.github.com/rest/repos/repos#get-a-repository"}

Exiting the challenge_processing_script.py script after failure
```