Add commission / commissionable-base columns to Metrics reservations export

Category:​ Reporting & Analytics (or Property Management / Mogul if available)

Description:
Property managers running multi-owner portfolios need to reconcile commission per reservation across all their owners in one report. Today, commission agreements are configured per property/owner under ​Your Business → Commission Agreements​ and only surface on Owner Statements — which are statement-level (per owner, per period), not per-reservation.

The Metrics → Reservations & Financials export is the natural place for per-reservation reconciliation, but it has a fixed schema and currently exposes nothing about the commission agreement applied to the booking's property/owner.

Requested:​ Two new opt-in columns on the Metrics reservations export:
• commissionable_base — the base the commission is calculated on for that reservation (per the property's active commission agreement at booking/checkout date)
• pm_commission — the resulting commission amount for that reservation

Bonus: an owner_id / owner_name column so PMs can group/filter the export by owner without going back to property metadata.

Why it matters:​ Lets PMs reconcile commission across all owners in a single export, matches how they actually do month-end accounting, and removes the need to manually join Metrics + per-owner Statements exports in a spreadsheet.