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.

.github/workflows/change-app-version.yml

@@ -33,6 +33,7 @@ on:
           - rallly
           - voucher-vault
           - minecraft-router
+          - minecraft-server
   workflow_call:
     inputs:
       app-version:

.github/workflows/publish-minecraft-server.yml

@@ -0,0 +1,15 @@
+name: Publish Minecraft-Server Helm Chart
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+    paths:
+      - minecraft-server/**
+jobs:
+  publish-minecraft-server:
+    name: Publish Minecraft-Server Helm Chart
+    uses: ./.github/workflows/publish-helm-chart.yml
+    with:
+      chart-name: 'minecraft-server'
+    secrets: inherit