Import minecraft-server chart for Fleet migration stage 1 (java8 line)

Imports the chart from cluster-config functionally unchanged, wires it into
the publish/validate/install-test pipelines and publishes it as the first of
three Java lines (0.4.0+upjava8).

The only deviation from the source chart is the chart-global scaleDown flag
plus a server.replicas value, following the satisfactory pattern: two of the
three servers stand at 0 replicas in the cluster, which the chart could not
express, and Fleet would otherwise start them on reconcile. The default
(scaleDown: false) still renders replicas: 1, so the rendering of the running
server is unchanged - verified byte-identical against the three real values
files for all three Java lines.

Known deficiencies (hardening, probes, naming scheme, hardcoded values,
missing icon, the misleading mc-router auto-discovery annotations) are left
untouched on purpose and are scheduled for stage 2.

minecraft-server/templates/_helpers.tpl

@@ -0,0 +1,35 @@
+{{/*
+Render the replica count for a Deployment/StatefulSet.
+
+Input: dict
+  "scaleDown"  the chart-global .Values.scaleDown flag (may be nil)
+  "replicas"   the workload's replicas value (may be nil)
+
+Rules (issue #25):
+  - scaleDown: true takes precedence and always yields 0.
+  - otherwise an explicitly set replicas value is used as given, including an
+    explicit 0 — Helm's "default" would swallow 0, hence the explicit
+    kindIs "invalid" nil check.
+  - a missing replicas value defaults to 1.
+
+Usage (the values path to the workload's replicas varies per chart):
+  replicas: {{ include "minecraft-server.replicas" (dict "scaleDown" .Values.scaleDown "replicas" .Values.server.replicas) }}
+
+NOTE: charts in this repo deliberately have no dependencies, so this helper is
+duplicated into every chart's templates/_helpers.tpl with the chart's name as
+define prefix. The reference implementation lives in template-chart.
+
+This chart is a stage-1 import (issue #67) and does not yet follow the repo
+conventions; only the replicas helper was taken over, because the scaleDown
+flag is needed before the Fleet migration. The resources helper follows in
+stage 2 together with the rest of the convention alignment.
+*/}}
+{{- define "minecraft-server.replicas" -}}
+{{- if .scaleDown -}}
+0
+{{- else if not (kindIs "invalid" .replicas) -}}
+{{- .replicas -}}
+{{- else -}}
+1
+{{- end -}}
+{{- end -}}