feat: improve Helm chart

[Trojan295]

This change is opinionated and unfortunately is a breaking change. Feel free to close the PR, if you don't like it.

Changes:

• Adds options to specify externalIPs for the Service. Useful in case you don't have a load balancer.
• Adds to provide an existing Secret with password. Useful if you use sealed-secrets or external-secrets.
• Refactors the structure of values. Moves service related keys under service key, image related keys under image and puts server configuration related values under config.

It also resolves https://github.com/jsknnr/enshrouded-server/issues/54