Add support for custom Helm chart repo, URL, and service name in Barbican exporter installer script

[vish6760]

Summary

This PR enhances the installer scripts to allow dynamic configuration of Helm chart repository name, repository URL, and service name through custom Helm override files.

Changes Introduced

• Added logic to parse chart metadata (repo_url, repo_name, service_name) from YAML files located under ${SERVICE_CUSTOM_OVERRIDES}.
• Introduced fallback defaults for all three variables if custom overrides are not provided.
• Enhanced Helm chart path resolution:
  Automatically detects OCI-based Helm registries (oci://)
  Falls back to traditional Helm repo handling with helm repo add and helm repo update.
• Added debug logs for visibility for (repo_url, repo_name, service_name).

Benefits

• Custom registry deployments by reading overrides dynamically.
• Reduces the need to modify core installer scripts when using private or organization-specific Helm registries.
• Improves debuggability and maintainability through explicit output and clean fallback handling.

[zhmarvi]

LGTM