feat: chart: allow specifying imagePullSecrets

[USA-RedDragon]

Context

• Allow specifying imagePullSecrets due to the Docker Hub ratelimit
• Related: feat: Publish to GHCR #353

Choices

• Docker Hub's rate limit is easily hit when running a large Kubernetes cluster, therefore it's prudent to allow users of the chart to authenticate to raise the rate limit.

Test instructions

1. helm template palworld ./palworld/ -f ./palworld/values.yaml --set 'server.image.imagePullSecrets[0].name=registry-docker-hub' then verified the imagePullSecrets on the Deployment was valid

Checklist before requesting a review

• I have performed a self-review of my code
• I've added documentation about this change to the README.
• I've not introduced breaking changes.

[Twinki14]

I'm going to go ahead and make this fix in the new helm-chart repository, Twinki14/palworld-server-chart#1

But I don't want to steal your thunder, so if you'd like to make a PR there I'd be happy to merge it!

[USA-RedDragon]

Feel free to put it in the helm chart yourself if it's easier, it's more important that the pull secrets be configurable than the idea that I get credit! Happy to do whatever's easiest!