Fix NPE during delivery

Type of change

• Bug Fix
• Feature

Please provide link to gitlab issue or ADR(Architecture Decision Record)

Does this introduce a change in the core logic?

• [NO]

Does this introduce a change in the cloud provider implementation, if so which cloud?

• AWS
• Azure
• Google Cloud
• IBM

Does this introduce a breaking change?

• [NO]

What is the current behavior?

Subscription configs do not contain secret values, NPE is produced during the event delivery to the end consumer.

What is the new/expected behavior?

Notification forcibly requests config with a secret from Register if it's not in the cache.

Have you added/updated Unit Tests and Integration Tests?

Any other useful information