Create EE only service GitlabSubscriptions::Members::ActivityService

What does this MR do and why?

This MR adds a new EE only service: GitlabSubscriptions::Members::ActivityService.

This will be used to track members related activity.

Related to #461338 (closed)

Databases

1. Getting single record, if exists

SELECT 1 AS one FROM "subscription_seat_assignments" WHERE "subscription_seat_assignments"."namespace_id" = 411 AND "subscription_seat_assignments"."user_id" = 109 LIMIT 1

PostgresAI: https://console.postgres.ai/gitlab/gitlab-production-main/sessions/31879/commands/98599

2. Creating a new record

INSERT INTO "subscription_seat_assignments" ("namespace_id", "user_id", "last_activity_on", "created_at", "updated_at") VALUES (411, 109, '2024-09-25 09:40:09.054561', '2024-09-25 09:40:09.057704', '2024-09-25 09:40:09.057704') RETURNING "id"

PostgresAI: https://console.postgres.ai/gitlab/gitlab-production-main/sessions/31879/commands/98602

3. Updating a record

UPDATE "subscription_seat_assignments" SET "last_activity_on" = '2024-09-25 09:43:05.804959', "updated_at" = '2024-09-25 09:43:05.831099' WHERE "subscription_seat_assignments"."id" = 2

PostgresAI: https://console.postgres.ai/gitlab/gitlab-production-main/sessions/31879/commands/98601

MR acceptance checklist

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