feat: add Helm Chart support with auto-generation from Kustomize

[ballista01]

Inspired by #95 (comment) I tried to add a Helm Chart support for etcd-operator. The Chart is auto-generated from Kustomize manifests to maintain a single source of truth.

Changes

Helm Chart Generation

• make helm generates Chart from Kustomize using helmify and yq
• Includes automatic helm lint validation
• Generated files excluded from git (Chart.yaml, values.yaml, templates/, crds/)

Deployment Methods

• E2E tests now support both Kustomize and Helm
• Use DEPLOY_METHOD env var: "kustomize", "helm", or "all" (default)
• Both methods deploy functionally identical operators

Documentation

• Added helm/README.md with usage guide
• Updated main README.md with deployment options
• Included example configs: values-ha.yaml (3 replicas, leader election) and values-minimal.yaml

Testing

• Unit tests for Chart generation, validation, and values
• E2E tests pass with both deployment methods
• Tested with cert-manager v1.19.1 and etcd v3.6.5
• Verified HA setup with 3-node cluster and leader election

Architecture

• Kustomize manifests remain the source of truth
• Helm Chart auto-generated during build/test (not committed)
• CRDs installed by Helm but not deleted on uninstall
• Tools (helmify, yq) auto-install

Breaking Changes

None. Existing Kustomize deployments work unchanged.

Closes #94

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: ballista01
Once this PR has been reviewed and has the lgtm label, please assign jmhbnz for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ballista01]

@ivanvc @ahrtr Here's my attempt with Helmify. Most of it is documentation (~400 lines), tests (~700 lines), and examples (~100 lines). Core logic is just ~100 lines in Makefile. Let me know if you prefer smaller PRs (e.g. keeping only makefile changes)

[ivanvc]

I did briefly review this. I believe it should be broken down into at least separate commits. Also, the README.md appears to point to another chart.

I'll come back to this after 0.2.0.