Add GraphQL support to sorting by storage_size

What does this MR do and why?

For Migrate admin area groups list to Vue shared co... (&17783 - closed) and Fix sorting by `storage_size` in GraphQL groups... (#552153 - closed)

We are working on moving Admin area -> Groups to Vue components with a GraphQL data source. When I was working on this I noticed that the GraphQL query did not support sorting by storage_size due to https://docs.gitlab.com/development/database/keyset_pagination/#complex-order-configuration.

This MR attempts to add support for sorting by storage_size while still supporting keyset pagination.

Database review

Optimization issue: Optimize groups storage size sorting in Admin Area (#556662)

Before: /admin/groups?sort=storage_size_desc

Click to expand

SELECT "namespaces".*, "statistics".*
FROM "namespaces",
     LATERAL (SELECT COALESCE(SUM("project_statistics"."storage_size"), 0)            AS storage_size,
                     COALESCE(SUM("project_statistics"."repository_size"), 0)         AS repository_size,
                     COALESCE(SUM("project_statistics"."wiki_size"), 0)               AS wiki_size,
                     COALESCE(SUM("project_statistics"."snippets_size"), 0)           AS snippets_size,
                     COALESCE(SUM("project_statistics"."lfs_objects_size"), 0)        AS lfs_objects_size,
                     COALESCE(SUM("project_statistics"."build_artifacts_size"), 0)    AS build_artifacts_size,
                     COALESCE(SUM("project_statistics"."pipeline_artifacts_size"), 0) AS pipeline_artifacts_size,
                     COALESCE(SUM("project_statistics"."packages_size"), 0)           AS packages_size,
                     COALESCE(SUM("project_statistics"."uploads_size"), 0)            AS uploads_size
              FROM "project_statistics"
              WHERE "project_statistics"."namespace_id" = "namespaces"."id") statistics
WHERE "namespaces"."type" = 'Group'
ORDER BY storage_size DESC, namespaces.id DESC
LIMIT 20 OFFSET 60 

After: GraphQL Query

Click to expand

SELECT "namespaces".*, "statistics".*
FROM "namespaces",
     LATERAL (SELECT COALESCE(SUM("project_statistics"."storage_size"), 0)            AS storage_size,
                     COALESCE(SUM("project_statistics"."repository_size"), 0)         AS repository_size,
                     COALESCE(SUM("project_statistics"."wiki_size"), 0)               AS wiki_size,
                     COALESCE(SUM("project_statistics"."snippets_size"), 0)           AS snippets_size,
                     COALESCE(SUM("project_statistics"."lfs_objects_size"), 0)        AS lfs_objects_size,
                     COALESCE(SUM("project_statistics"."build_artifacts_size"), 0)    AS build_artifacts_size,
                     COALESCE(SUM("project_statistics"."pipeline_artifacts_size"), 0) AS pipeline_artifacts_size,
                     COALESCE(SUM("project_statistics"."packages_size"), 0)           AS packages_size,
                     COALESCE(SUM("project_statistics"."uploads_size"), 0)            AS uploads_size
              FROM "project_statistics"
              WHERE "project_statistics"."namespace_id" = "namespaces"."id") statistics
WHERE "namespaces"."type" = 'Group'
ORDER BY storage_size DESC, "namespaces"."id" DESC
LIMIT 101

Screenshots or screen recordings

No visual changes

How to set up and validate locally

1. Sign in as an admin user.
2. Go to /-/graphql-explorer
3. Run the following query

{
  groups(allAvailable: true, sort: "storage_size_keyset_desc") {
    nodes {
      fullName
      projectStatistics {
        storageSize
      }
    }
  }
}

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