feat: configurable minimum notice period before a supplier can request a shipment pause

[shakurJJ]

Summary

A supplier can request a shipment pause (request_shipment_pause) at any time with no minimum lead time, which lets a supplier stall a shipment on short notice right before a milestone deadline. This proposes an admin-configurable minimum notice period.

Proposed Behaviour

• Admin sets a minimum notice period (in ledgers) between the current ledger and the next upcoming milestone deadline.
• request_shipment_pause rejects the request if the shipment's next milestone deadline is closer than the configured notice period.
• Default value preserves today's behaviour (no minimum notice) unless explicitly configured.

Acceptance Criteria

• Admin can set/get the minimum pause notice period
• Pause request within the notice window is rejected with a clear error
• Pause request outside the notice window succeeds as today
• Tests cover both paths

[Abdulidris6]

@Abdulidris6 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I reviewed the issue and followed the relevant code paths to understand the situation. I have a clear plan for the fix and will take care to avoid unintended regressions.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Abdulidris6 to this issue.