Expose Alternate Schedule and pre-stage scale-in delay via the Auto-Scale REST API

Problem
Organizations managing NME via REST API (IaC, automation pipelines, scripted configuration management) cannot fully control Auto-Scale configuration through the API alone. Two fields visible and configurable in the NME web console are absent from the /api/v1/arm/hostpool/{subscriptionId}/{resourceGroup}/{hostPoolName}/auto-scale endpoint:

1. Alternate Schedule — the secondary template's isEnabled toggle, weekDays array, and all associated capacity, scaling logic, scale-in restriction, rolling drain, and pre-stage settings are not present in the GET response and are not accepted via PUT/PATCH.
2. Pre-stage hosts scale-in delay — the per-config "Scale in delay" field (hours + minutes, visible in the GUI under each Pre-Stage Hosts config entry) is absent from the preStageHosts.configs[] objects returned by the API. The field does not round-trip through GET/PUT; any value set in the GUI is invisible and unmodifiable via API.

Description
Add Alternate Schedule fields and the pre-stage scaleInDelay field to the Auto-Scale REST API endpoint so the complete auto-scale configuration can be managed programmatically without requiring GUI fallback for these two specific settings.

Vision

• GET /api/v1/arm/hostpool/.../auto-scale should return the full Alternate Schedule object (mirroring the Default Schedule structure) including isEnabled, weekDays, capacity settings, scaling logic, scale-in restriction, rolling drain, and pre-stage configs.
• PUT/PATCH to the same endpoint should accept and persist changes to all Alternate Schedule fields.
• Each preStageHosts.configs[] entry should include a scaleInDelayHours and/or scaleInDelayMinutes field that round-trips correctly through GET/PUT.
• Changes should be additive and non-breaking — existing PUT bodies that omit the new fields preserve current behavior.