fix(litmus-agent): fix hook secret name mismatch and subscriber subchart dependency

[pierluigilenoci]

Summary

• Replace all subscriber.* template helper references in parent chart templates with litmus-agent.* equivalents
• Fix hook secret name mismatch between creation (subscriber.fullname) and reference (litmus-agent.fullname)
• Fix chart rendering failure when subscriber.enabled: false
• Update values.yaml comment to reference the correct helper

Problem

The litmus-agent parent chart was using helper templates defined in the subscriber subchart:

File	Was using	Now uses
templates/secret.yaml	subscriber.fullname	litmus-agent.fullname
templates/infra-secret.yaml	subscriber.labels	litmus-agent.labels
templates/infra-config-map.yaml	subscriber.labels	litmus-agent.labels
templates/infra-config-map-workflow.yaml	subscriber.labels	litmus-agent.labels

This caused:

1. Secret name mismatch — the hook secret was created as <release>-subscriber-hook but the pre-install job referenced <release>-litmus-agent-hook
2. Render failure — setting subscriber.enabled: false caused helm template to fail because the subscriber subchart's _helpers.tpl was not loaded

Verification

# Both pass after the fix:
helm template test-release charts/litmus-agent
helm template test-release charts/litmus-agent --set subscriber.enabled=false

Closes #418

Test plan

• helm template succeeds with default values
• helm template succeeds with subscriber.enabled=false
• Hook secret name matches between secret.yaml and hook-pre-install-job.yaml

[pierluigilenoci]

@Jonsy13 @ispeakc0de this is ready for review.

The fix replaces all subscriber.* helper references in the parent chart with litmus-agent.* equivalents (4 files). Verified with helm template in both subscriber.enabled=true and subscriber.enabled=false configurations.

Let me know if you'd like any changes!

[pierluigilenoci]

@ksatchit @imrajdas @cnd4 could you please review this when you get a chance? Thanks!