configurable retry frequency for subscription renewals

Current: merchants can only set the recovery window (1–30 days). The retry schedule is fixed at 12 h → 24 h → 48 h → 72 h…, which means 1 retry on day 1 and 2 by day 3.

Request: let merchants set the retry frequency, or retry more often in the first few days (for example daily for days 1–4), especially for insufficient-funds declines.

Why: insufficient-funds declines often clear within a few days, when the customer is paid or tops up. More frequent early retries would recover more of these payments before the subscription stays on hold.