feat(helm): Add self-hosting Helm chart for Svix webhook service

[adityawdubey]

Motivation

Svix does not provide an official or supported Helm chart for self-hosting. Users looking to deploy Svix on Kubernetes must manually provision the backend, database, Redis, and other components, often leading to fragmented, error-prone, or insecure setups.

This makes it harder for DevOps teams to adopt Svix in environments where Kubernetes and Helm are standard deployment tools. Without a reusable Helm chart, managing upgrades, scaling, or secure configuration becomes more difficult and inconsistent across teams.

Solution

This PR introduces a fully functional Helm chart to deploy the entire Svix webhook stack on Kubernetes. It includes:

• Templates for the Svix backend, PostgreSQL, PgBouncer, and Redis
• Support for external database endpoints
• Configurable values for secrets and resourcesBuilt-in health checks
• Built-in health checks, service definitions, and PVC support
• Horizontal Pod Autoscaler (HPA) for svix-backend based on CPU and memory utilization, enabling automatic scaling under load
• A comprehensive README.md with deployment guidance and production best practices
• Added .gitignore for Helm chart to exclude rendered files and secrets

This addition allows users to self-host Svix reliably, reproducibly, and securely using Helm — supporting both local testing and production deployments out of the box.