Break repository excess calculation into smaller, simpler queries [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

The repository execess calculation's query involves a subquery of getting all nested groups. This resulted in some slow query during one incident (but it is not the cause).

We want to separate the split nested groups query as a separate query, which should be more resilient when things go wrong.

The more detailed analysis can be found here: https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12769#note_525534422

From research, one of the larger group contains 5000 sub-groups. A feature flag is added so we can test if this is okay, or if we need to further split the query.

Related issue #323985 (closed)

Database query

Query example: group.total_repository_size_excess

before change

SELECT 
  SUM(
    (
      (
        "project_statistics"."repository_size" + "project_statistics"."lfs_objects_size"
      ) - "projects"."repository_size_limit"
    )
  ) 
FROM 
  "projects" 
  INNER JOIN "project_statistics" ON "project_statistics"."project_id" = "projects"."id" 
WHERE 
  "projects"."namespace_id" IN (
    WITH RECURSIVE "base_and_descendants" AS (
      (
        SELECT 
          "namespaces".* 
        FROM 
          "namespaces" 
        WHERE 
          "namespaces"."type" = 'Group' 
          AND "namespaces"."id" = 22
      ) 
      UNION 
        (
          SELECT 
            "namespaces".* 
          FROM 
            "namespaces", 
            "base_and_descendants" 
          WHERE 
            "namespaces"."type" = 'Group' 
            AND "namespaces"."parent_id" = "base_and_descendants"."id"
        )
    ) 
    SELECT 
      id 
    FROM 
      "base_and_descendants" AS "namespaces"
  ) 
  AND (
    "project_statistics"."repository_size" + "project_statistics"."lfs_objects_size"
  ) > "projects"."repository_size_limit" 
  AND "projects"."repository_size_limit" != 0

after change

WITH RECURSIVE "base_and_descendants" AS (
  (
    SELECT 
      "namespaces".* 
    FROM 
      "namespaces" 
    WHERE 
      "namespaces"."type" = 'Group' 
      AND "namespaces"."id" = 22
  ) 
  UNION 
    (
      SELECT 
        "namespaces".* 
      FROM 
        "namespaces", 
        "base_and_descendants" 
      WHERE 
        "namespaces"."type" = 'Group' 
        AND "namespaces"."parent_id" = "base_and_descendants"."id"
    )
) 
SELECT 
  id 
FROM 
  "base_and_descendants" AS "namespaces"


SELECT 
  SUM(
    (
      (
        "project_statistics"."repository_size" + "project_statistics"."lfs_objects_size"
      ) - "projects"."repository_size_limit"
    )
  ) 
FROM 
  "projects" 
  INNER JOIN "project_statistics" ON "project_statistics"."project_id" = "projects"."id" 
WHERE 
  "projects"."namespace_id" = 22 
  AND (
    "project_statistics"."repository_size" + "project_statistics"."lfs_objects_size"
  ) > "projects"."repository_size_limit" 
  AND "projects"."repository_size_limit" != 0

Does this MR meet the acceptance criteria?

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• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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• Label as security and @ mention @gitlab-com/gl-security/appsec
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