Add option for extra init containers for Traefik

[gregingenii]

Proposed change

Bourne out of race conditions with deploying other resources at the same time, a solution for us has been to run an init container to delay the traefik container. Currently we can't define any extra init containers (some already exist), so this change will allow users to define this, or any other, extra init containers.

Alternative options

• Manual restarting of the traefik container after deployment, which is cumbersome
• Manual change of the chart locally, requiring us to manage the sync between the repository and our deployment

Who would use this feature?

Anyone running into similar race conditions, or indeed any problem that could be solved with another init container for traefik

(Optional): Suggest a solution

I have opened a PR with a potential solution: https://github.com/jupyterhub/zero-to-jupyterhub-k8s/pull/2670

[welcome[bot]]

Thank you for opening your first issue in this project! Engagement like this is essential for open source projects! :hugs:
If you haven't done so already, check out Jupyter's Code of Conduct. Also, please try to follow the issue template as it helps other other community members to contribute more effectively. You can meet the other Jovyans by joining our Discourse forum. There is also an intro thread there where you can stop by and say Hi! :wave:
Welcome to the Jupyter community! :tada:

[consideRatio]

Closed by #2670