Improvements to gift card mails (RTC-31580)

When gift card is being sent by an e-mail, then in the received message, the amount field contains two decimals and date field shows only the date (without time).

Multi-country: Import of countries (RTC-32293)

Store groups' country codes are imported from Store Service to the GiftCard Service.

Technology framework (RTC-29202)

GiftCardService is migrated to .NET 6.