feat: add nameOverride and fullnameOverride to minecraft chart

[joryirving]

Adds nameOverride and fullnameOverride to the chart/helpers, as per the mc-router chart.

Closes #252

[billimek]

Thanks @joryirving! Can you please bump the chart version in Chart.yaml such that the new version is 4.25.0 given that this is a new feature?

[janpfischer]

Since this change I get the following error message when trying to deploy the new chart version:

'Helm upgrade failed for release selfhosted/minecraft with chart minecraft@4.26.1:
      template: minecraft/templates/_helpers.tpl:32:14: executing "minecraft.fullname"
      at <.Values.fullnameOverride>: nil pointer evaluating interface {}.fullnameOverride'

I do not set a fullname in my values. I believe it has something to do with nameOverwrite and fullNameOverwrite are set to "" in values.yaml per default and the logic in the if-clauses.