feat(helm): add DOI service chart

[WenbinWL]

Summary

Add an initial Helm chart for deploying the CADC DOI service to Kubernetes.

The chart is based on the DOI source configuration and is intended to support
migration from the existing Docker Swarm deployment. Current Swarm deployment
details still need to be reviewed before the chart is considered ready for
deployment.

Kubernetes resources

The chart currently defines:

• Deployment
• Service
• Ingress
• ServiceAccount
• ConfigMap
• External Secret references
• Helm connectivity test

Information required from the current deployment

• Confirm container image repository, tag, digest, and architecture
• Confirm active runtime configuration files
• Confirm certificate/credential filenames and mount paths
• Confirm which values must be managed as Kubernetes Secrets
• Confirm hostname, Ingress class, and forwarded certificate headers
• Confirm target namespace and image pull credentials
• Confirm container security context and resource requirements
• Validate the chart against the existing Docker Swarm configuration

[at88mph]

Moved to doi repository.