[PM-26682] [Milestone 2d] Display discount on subscription page (#17229)

* The discount badge implementation

* Use existing flag

* Added the top spaces as requested

* refactor: move discount-badge to pricing library and consolidate discount classes

* fix: add CommonModule import to discount-badge component and simplify discounted amount calculation

- Add CommonModule import to discount-badge component for *ngIf directive
- Simplify discountedSubscriptionAmount to use upcomingInvoice.amount from server instead of manual calculation

* Fix the lint errors

* Story update

---------

Co-authored-by: Alex Morask <amorask@bitwarden.com>

libs/common/src/enums/feature-flag.enum.ts

@@ -33,6 +33,7 @@ export enum FeatureFlag {
   PM26793_FetchPremiumPriceFromPricingService = "pm-26793-fetch-premium-price-from-pricing-service",
   PM23713_PremiumBadgeOpensNewPremiumUpgradeDialog = "pm-23713-premium-badge-opens-new-premium-upgrade-dialog",
   PM26462_Milestone_3 = "pm-26462-milestone-3",
+  PM23341_Milestone_2 = "pm-23341-milestone-2",
 
   /* Key Management */
   PrivateKeyRegeneration = "pm-12241-private-key-regeneration",
@@ -129,6 +130,7 @@ export const DefaultFeatureFlagValue = {
   [FeatureFlag.PM26793_FetchPremiumPriceFromPricingService]: FALSE,
   [FeatureFlag.PM23713_PremiumBadgeOpensNewPremiumUpgradeDialog]: FALSE,
   [FeatureFlag.PM26462_Milestone_3]: FALSE,
+  [FeatureFlag.PM23341_Milestone_2]: FALSE,
 
   /* Key Management */
   [FeatureFlag.PrivateKeyRegeneration]: FALSE,