Minecraft-router chart: naming scheme, hardening, probes, values interface

Stage 2 of the Fleet migration for minecraft-router: bring the chart up to the
repo style guidelines. Chart 0.1.1+up1.25.1 -> 1.0.0+up1.25.1 (major: resource
renames, mappings becomes required, probes and security hardening change the
runtime behavior; appVersion unchanged).

- Resources renamed to {{ .Release.Name }}-{{ .Chart.Name }}-<kind>, templates
  to <chart>.<kind>.yaml; the deployment label now matches its own selector.
- mappings is required and must not be empty (the old default rendered
  "<nil>": "<nil>:25565"); every entry needs domain and internalUrl.
- Ports come from values: server.port (router listen port, also passed as
  --port), server.backendPort (default backend port, overridable per mapping),
  server.apiPort (--api-binding, used by the probes). Defaults stay 25565 /
  25565 / 8080, server.outwardPort keeps its 25565 default and comment.
- _helpers.tpl added (resources/limitFactor and replicas/scaleDown helpers),
  resources come from values, no CPU limit.
- replicas value plus the chart-global scaleDown flag.
- Additive env block rendered through tpl (value / secretKeyRef /
  configMapKeyRef).
- Values-configurable securityContext.pod / .container with hardened defaults:
  non-root uid/gid 10000, readOnlyRootFilesystem, no privilege escalation, all
  capabilities dropped.
- Liveness, readiness and startup probes on the mc-router API: GET /routes with
  an "Accept: application/json" header (the API router matches on that header
  and answers 404 without it).
- icon added to Chart.yaml.
- CI fixture supplies mappings; README chart table entry updated.

minecraft-router/templates/minecraft-router.configmap.yaml

@@ -0,0 +1,22 @@
+{{- $message := "minecraft-router: .Values.mappings is required and must not be empty - set at least one mapping with a domain and an internalUrl (see values.yaml)" -}}
+{{- $mappings := required $message .Values.mappings -}}
+{{- if and (not (kindIs "invalid" $mappings)) (or (not (kindIs "slice" $mappings)) (empty $mappings)) }}{{- fail $message -}}{{- end -}}
+{{- $routes := dict -}}
+{{/* "helm lint" reports a missing required value but keeps rendering, so the
+     loop has to tolerate the nil it hands back; "helm template" and "helm
+     install" abort on the required above. */}}
+{{- range $index, $mapping := ($mappings | default list) -}}
+{{- $domain := required (printf "minecraft-router: .Values.mappings[%d].domain is required" $index) $mapping.domain -}}
+{{- $internalUrl := required (printf "minecraft-router: .Values.mappings[%d].internalUrl is required" $index) $mapping.internalUrl -}}
+{{- $port := $mapping.port | default $.Values.server.backendPort -}}
+{{- $_ := set $routes $domain (printf "%v:%v" $internalUrl $port) -}}
+{{- end -}}
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: {{ .Release.Name }}-{{ .Chart.Name }}-configmap
+  labels:
+    app: {{ .Release.Name }}-{{ .Chart.Name }}-configmap
+data:
+  custom-routing-config.json: |
+{{ dict "mappings" $routes | toPrettyJson | indent 4 }}