Support per-customer usage limits and customer-targeted discount codes

Request: Add features to Advanced Discount Code campaigns to allow merchant-controlled usage limits and customer targeting. Requirements:

• Per-customer usage limits (e.g., limit code to 1 use per customer).

• First-time-customer / new-subscriber targeting (ability to restrict a code to customers who have never purchased or who are in a subscriber list).

• Ability to target by customer tags / email lists / segments.

• Optional total usage limits (e.g., first X uses) and combined usage controls (per-customer + total uses).

Notes: Discounty already supports discount codes, scheduling, product/collection inclusion and exclusions, and mixed-module campaigns. These additions would enable the merchant's two requested campaigns (a 10% code limited to new subscribers / one-time use, and a time-limited weekend 10% code) to be created as codes with exclusions and schedules.