Update subscriptionUsage query

What does this MR do and why?

Update subscriptionUsage query

• Rename lastUpdated to lastEventTransactionAt
• Add oneTimeCredits node
• Add usersUsage.creditsUsed

This is part of an ongoing effort. One of the related issues is https://gitlab.com/gitlab-org/gitlab/-/issues/577984

References

This work is divided in 3 main issues:

• Architectural discussions: https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/13779
  • How we approached this in the PoC
• API on CustomersDot side: https://gitlab.com/gitlab-org/gitlab/-/issues/565808
• API on GitLab side: https://gitlab.com/gitlab-org/gitlab/-/issues/567987

PoC:

• Demo video
• code (although things here are a bit different)
  • GitLab: https://gitlab.com/gitlab-org/fulfillment/gitlab/-/merge_requests/6
  • CustomersDot: https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/13259

Screenshots or screen recordings

N/A

How to set up and validate locally

1. These fields rely on CustomersDot code that isn't merged just yet, so the easiest way to test this is to mock the CDot response:

Mocked response patch

diff --git a/ee/lib/gitlab/subscription_portal/subscription_usage_client.rb b/ee/lib/gitlab/subscription_portal/subscription_usage_client.rb
index dd09383d3240..63588fe004e1 100644
--- a/ee/lib/gitlab/subscription_portal/subscription_usage_client.rb
+++ b/ee/lib/gitlab/subscription_portal/subscription_usage_client.rb
@@ -180,6 +180,10 @@ def initialize(
       end

       def get_metadata
+        return {
+          success: true,
+          subscriptionUsage: { lastEventTransactionAt: 2.hours.ago }
+        }
         response = execute_graphql_query(
           query: GET_METADATA_QUERY,
           variables: default_variables
@@ -197,6 +201,13 @@ def get_metadata
       strong_memoize_attr :get_metadata

       def get_one_time_credits
+        return {
+          success: true,
+          oneTimeCredits: {
+            totalCredits: 543.21,
+            creditsUsed: 123.45
+          }
+        }
         response = execute_graphql_query(
           query: GET_ONE_TIME_CREDITS_QUERY,
           variables: default_variables.merge(startDate: start_date, endDate: end_date)
@@ -285,6 +296,10 @@ def get_usage_for_user_ids(user_ids)
       end

       def get_users_usage_stats
+        return {
+          success: true,
+          usersUsage: { creditsUsed: 111.22 }
+        }
         response = execute_graphql_query(
           query: GET_USERS_USAGE_STATS_QUERY,
           variables: default_variables.merge(startDate: start_date, endDate: end_date)

2. Then open GraphQL explorer and execute this query (https://gdk.test:3443/-/graphql-explorer)

GraphQL query

query getSubscriptionUsage($namespacePath: ID) {
  subscriptionUsage(namespacePath: $namespacePath) {
    lastEventTransactionAt
    oneTimeCredits {
      totalCredits
      creditsUsed
    }
    usersUsage {
      creditsUsed
    }
  }
}

MR acceptance checklist

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