fix(Employee): make approver setting more flexible

[PatrickDEissler]

Fix:
Don't always set the approver fields based on reports_to. Only set if empty. This way, we avoid empty approvers and set some sort of default.

But:
We allow users to change the approvers to someone else.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no concrete blocking or independently actionable non-blocking issues identified.

The changed fallback assignment preserves configured approvers while still populating empty fields from Reports To, and the accompanying property setters and translation updates are consistent with that behavior.

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