Metadata Defaults for Silent Document Uploads

Problem
Administrators can configure default or fixed (mandatory) metadata values for documents uploaded via the UI. For documents uploaded via silent drops, only fixed values are supported; default values cannot be configured. This results in inconsistent behavior between UI uploads and silent drops and limits flexibility for automated ingestion. Metadata enrichment for silent drops is therefore either too rigid (fixed values only) or depends on external solutions to ensure required metadata is set.

Desired Solution
Extend silent-drop metadata configuration to support default values alongside fixed values:
- Scenario 1 – Default value, not fixed
• No value provided → apply default
• Value provided → retain provided value
- Scenario 2 – Default value, fixed
• No value provided → apply default (fixed)
• Value provided → override with default (fixed)