NIFI-15910 Improve Connector Secret verification

[kevdoran]

Summary

NIFI-15910

When a connector configuration contains a SECRET_REFERENCE whose fields (fullyQualifiedSecretName, secretName) are unpopulated — either because the property is gated by another property whose dependency isn't satisfied, or because it's a placeholder default emitted by an external ConnectorConfigurationProvider — StandardConnectorNode is eagerly resolving it against the SecretsManager and surfacing Property Validation - Secret Reference: The referenced secret [null] could not be found.

This change makes StandardConnectorNode.resolvePropertyReferences (and the matching validatePropertyReferences step traversal) skip secret resolution for two cases:

1. Properties whose ConnectorPropertyDependency isn't satisfied — using the same algorithm as AbstractConnector.isDependencySatisfied()
2. Structurally-empty SECRET_REFERENCE values where neither FQN nor secret name is populated. Empty stubs are treated as unset, so the connector's own required-property check produces the actionable is required message.

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