[Feature] Add an official Helm chart for distributed HStore deployment

[bitflicker64]

Feature Description

Apache HugeGraph ships container images and Compose deployments, but it does
not currently provide an official Helm installation path for the distributed
PD + Store + Server topology on Kubernetes.

The main challenge is encoding the distributed startup and recovery contract,
not only rendering Kubernetes resources:

• PD must reach Raft quorum before Store registers.
• Server must not run concurrent init-store operations against the same
  distributed backend.
• Store addresses can change after rescheduling, so DNS and gRPC clients must
  recover rather than retain stale addresses or channels.
• StatefulSet and PVC identities must remain stable when replica counts change.

Proposal

Add an application chart under helm/hugegraph that provides:

• PD and Store StatefulSets with persistent storage and headless Services.
• A Server Deployment with a client Service, optional HPA, PDB, and Ingress.
• PD, Store, and Server scheduling, resource, security, and ServiceAccount
  controls.
• PodDisruptionBudgets for the stateful components.
• A helm test connection check.
• values.schema.json validation so invalid combinations fail during render.
• Default, single-node, and production-oriented values presets.
• An optional Hubble UI component: single replica, pd (PD discovery with
  the cluster operations view) or direct wiring mode, optional Ingress and
  H2 persistence, wired to the deployed cluster. Current Hubble images
  authenticate their login against the cluster, so the chart requires
  server.auth when Hubble is enabled unless explicitly overridden.
• Helm lint, render, schema, compatibility, packaging, and kubeconform CI.
• Installation, configuration, upgrade, troubleshooting, and limitations
  documentation.

The chart configures the existing HugeGraph images. It does not vendor or
duplicate server-side implementation.

The implementation is #3132.

Prerequisites

The first chart release is version 0.1.0. While its PR is a draft, the chart
tracks the latest HugeGraph images. Before stable publication, the image tags
and appVersion will be pinned to the next HugeGraph release.

Three prerequisites have merged:

PR	Required behavior	Merged as
#3128	One gRPC stub binding per channel	b026a90a
#3129	Store readiness retries across all configured PD peers	8b2932c7
#3105	Bounded port preflight without requiring lsof	09dbc744

Three remain open:

PR	Required behavior	Current head
#3119	Dedicated init_store.enabled gate for distributed Server startup (issue #3118)	edf07d0f
#3126	Finite JVM DNS cache TTL, plus startup DNS-policy validation and JDK 24+ security-check handling	b40c42fb
#3130	Channel and stub refresh after a Store address change	198de19e

#3126 and #3130 form one recovery path: channel refresh cannot resolve a new
Store address while the JVM retains the old DNS result indefinitely.

#3119 has since been narrowed to the init_store.enabled option and its gate.
The Docker entrypoint and auth-bootstrap work that previously shared its branch
is now tracked separately in #3133. The chart does not depend on #3133 landing
first, but the entrypoint contract it describes is the one this chart relies on
for PASSWORD and auth.admin_pa handling.

Validation

The implemented chart was tested on a four-node Kubernetes cluster using a
3 PD + 3 Store + 3 Server topology, against a composition built from these
exact prerequisite heads:

PR	Head under test	Status now
#3105	ee8f5559	superseded by 09dbc744
#3119	3e505a81	superseded by ff1325ac
#3126	35e1a240	superseded by 4d0ff03e
#3128	0118e158	merged unchanged at this head
#3129	575a1122	merged at 61407213, one commit further
#3130	26218cb3	superseded by ddeef7a9

The completed validation covers:

• Static chart validation: PASS=239 FAIL=0 SKIP=0.
• Edge and hardening validation: PASS=37 FAIL=0.
• Fresh install with 9 Ready Pods and zero restarts.
• Same-package Helm upgrade with cluster and dataset checks passing.
• Server replacement: PASS=91 FAIL=0.
• Store replacement: PASS=90 FAIL=0, with data preserved.
• Deterministic PD REST failover: PASS=7 FAIL=0, followed by successful
  restoration.
• Legacy --reuse-values rendering and client-side dry-run compatibility.

The auth bootstrap fix (the wrapper now writes auth.admin_pa from the auth
Secret) and the Hubble component were validated separately against a newer
composition of master at 1716c774 plus the current heads of #3119,
#3126, and #3130; details are in the PR. The full lifecycle matrix rerun is
still pending before the PR leaves draft.

Only #3128 merged at exactly the head under test, so this matrix is the current
evidence baseline rather than a statement about today's master. It will be
rerun against a composition of the then-current heads before the chart PR
leaves draft.

Known gap

With init_store.enabled=false, the built-in authenticator's admin is created
on the PD startup path from auth.admin_pa, and Docker PASSWORD is discarded
because init-store reads it from stdin and the disabled path returns first.
The chart's wrapper currently writes only usePD and pd.peers, so an
auth-enabled deployment silently ignores the configured Secret today, and will
fail closed at container start once #3119 merges. The wrapper needs to write
auth.admin_pa from the same Secret. This is tracked on #3132 and must be
fixed and retested before that PR leaves draft.

Scope and follow-ups

This contribution establishes the official Helm installation path. TLS,
backup and restore, an Operator, multi-cluster orchestration, automatic leader
transfer, ConfigMap-based component configuration, and a complete monitoring
stack remain separate follow-up work and are documented as limitations.

Entrypoint property handling for mounted and upgraded configs is tracked in
#3133 and is outside this chart's scope.

The chart PR should remain a draft while its prerequisite PRs are open. Before
it is marked ready, it will be rebased onto the then-current master, composed
with the merged prerequisites, and the affected validation matrix will be run
again.

Related upstream issues

• #3135 PD: periodic partition leader balancing, motivated by fault testing chart deployments.

• #3136 Store: shard recovery metrics (sync progress, raft lag), motivated by fault testing chart deployments.

• #3137 PD-orchestrated graph creation: new graphs are not consistently available across Server replicas; the chart documents the window as a limitation.

  Update: the first server-side fix from the [Feature] Orchestrate graph creation through PD: new graphs are not consistently available across Server replicas ("Could not rebind [g]") #3137 roadmap (the creating server waits for its own graph binding before returning 200) is up in #3138.