[PM 33923]Add support for multiple organization discounts to organization subscription page

[cyprain-okeke]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-33923

📔 Objective

The organization subscription page previously only supported a single discount (CustomerDiscount). This PR updates the billing infrastructure to support multiple concurrent
discounts (CustomerDiscounts) — for example, a customer may have both a Milestone 2 migration discount and a Secrets Manager standalone discount at the same time.

Changes

API Response Models:

• OrganizationSubscriptionResponseModel — changed CustomerDiscount (single) to CustomerDiscounts (array). Organization pages pass through all discounts unfiltered so admins
  can see migration (M3/Families), SM standalone, and M2 discounts.
• SubscriptionResponseModel — changed to CustomerDiscounts array, still filtered to M2-only for the individual user subscription page.

Core Billing:

• SubscriptionInfo.CustomerDiscount → SubscriptionInfo.CustomerDiscounts (list).
• StripePaymentService.GetSubscriptionAsync — collects customer-level and subscription-level discounts into a single list, deduplicating by coupon ID. Phase 2 schedule
  discounts are merged/overridden rather than replacing the whole discount.
• GetBitwardenSubscriptionQuery — cart-level and product-level discounts are now lists; schedule phase 2 discounts return multiple entries; tax estimation passes multiple
  coupon IDs to Stripe's upcoming invoice API.
• Cart / CartItem — Discount → Discounts (list) to model multiple discounts per item or per cart.

📸 Screenshots

[codecov]

Codecov Report

❌ Patch coverage is 73.46939% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.14%. Comparing base (901bb67) to head (7596c77).

Files with missing lines	Patch %	Lines
...g/Services/Implementations/StripePaymentService.cs	78.78%	5 Missing and 2 partials ⚠️
...esponse/Organizations/OrganizationResponseModel.cs	0.00%	4 Missing ⚠️
...Api/Billing/Controllers/OrganizationsController.cs	0.00%	1 Missing ⚠️
...c/Api/Models/Response/SubscriptionResponseModel.cs	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7531   +/-   ##
=======================================
  Coverage   59.14%   59.14%           
=======================================
  Files        2077     2077           
  Lines       91864    91894   +30     
  Branches     8178     8180    +2     
=======================================
+ Hits        54331    54352   +21     
- Misses      35601    35608    +7     
- Partials     1932     1934    +2     

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[github-actions]

Checkmarx One – Scan Summary & Details – ae23a18e-0a79-4674-a173-5e92a5dfc8b0

Great job! No new security vulnerabilities introduced in this pull request

[amorask-bitwarden]

❌ There's quite a few changes here to the GetBitwardenSubscriptionQuery, which is currently only utilized for Premium. Multiple premium discounts is being addressed in PM-35121, so I believe this PR's scope extends too far. Can you ensure the changes are specifically focused on surfacing multiple organization discounts?

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[amorask-bitwarden]

Good work - still a few things we can remove though to tighten it up.

[amorask-bitwarden]

Suggested change

	if (subscriptionInfo?.CustomerDiscounts.Any(d => d.Id == StripeConstants.CouponIDs.SecretsManagerStandalone) != true)
	if (subscriptionInfo?.CustomerDiscounts.Any(d => d.Id != StripeConstants.CouponIDs.SecretsManagerStandalone))

[amorask-bitwarden]

Thanks for clearing up my question. Changes look good. Nice work!