Use linear version GroupsWithTemplatesFinder#extended_group_search

What does this MR do and why?

In this MR, we're switching the behavior of the GroupsWithTemplatesFinder#extended_group_search method to use the linear version. The new behavior is behind the linear_groups_template_finder_extended_group_search_ancestors_scopes feature flag.

How to set up and validate locally

1. Enable the setting check_namespace_plan

   Gitlab::CurrentSettings.update(check_namespace_plan: true)

2. Enable the new method behavior feature flag

   Feature.enable(:linear_groups_template_finder_extended_group_search_ancestors_scopes)

3. Enable the feature flag for linear ancestors scopes

   Feature.enable(:use_traversal_ids_for_ancestor_scopes)

4. In Rails console enable the traversal id feature flag

   Feature.enable(:use_traversal_ids)

5. In Rails console, execute:

GroupsWithTemplatesFinder.new.execute

SQL Query

The former SQL query was:

WITH RECURSIVE "base_and_ancestors" AS (
                                          (SELECT *
                                           FROM "namespaces"
                                           WHERE "namespaces"."type" = 'Group'
                                             AND "namespaces"."custom_project_templates_group_id" IS NOT NULL)
                                        UNION
                                          (SELECT *
                                           FROM "namespaces",
                                                "base_and_ancestors"
                                           WHERE "namespaces"."type" = 'Group'
                                             AND "namespaces"."id" = "base_and_ancestors"."parent_id"))
SELECT *
FROM "base_and_ancestors" AS "namespaces"
WHERE (EXISTS
         (SELECT 1
          FROM "plans"
          INNER JOIN "gitlab_subscriptions" ON "gitlab_subscriptions"."hosted_plan_id" = "plans"."id"
          WHERE "plans"."name" IN ('silver',
                                   'premium',
                                   'premium_trial',
                                   'gold',
                                   'ultimate',
                                   'ultimate_trial')
            AND (gitlab_subscriptions.namespace_id = namespaces.id)))

This is the query plan and the times are:

Time: 42.387 ms
  - planning: 1.335 ms
  - execution: 41.052 ms
    - I/O read: 0.000 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 16588 (~129.60 MiB) from the buffer pool
  - reads: 0 from the OS file cache, including disk I/O
  - dirtied: 0
  - writes: 0

The new SQL query is:

SELECT *
FROM
  (SELECT *
   FROM "namespaces"
   WHERE "namespaces"."type" = 'Group'
     AND "namespaces"."id" IN
       (SELECT unnest(traversal_ids)
        FROM "namespaces"
        WHERE "namespaces"."type" = 'Group'
          AND "namespaces"."custom_project_templates_group_id" IS NOT NULL)) namespaces
WHERE "namespaces"."type" = 'Group'
  AND (EXISTS
         (SELECT 1
          FROM "plans"
          INNER JOIN "gitlab_subscriptions" ON "gitlab_subscriptions"."hosted_plan_id" = "plans"."id"
          WHERE "plans"."name" IN ('silver',
                                   'premium',
                                   'premium_trial',
                                   'gold',
                                   'ultimate',
                                   'ultimate_trial')
            AND (gitlab_subscriptions.namespace_id = namespaces.id)))

This is the query plan and the times are:

Time: 40.253 ms
  - planning: 1.268 ms
  - execution: 38.985 ms
    - I/O read: 0.000 ms
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 21200 (~165.60 MiB) from the buffer pool
  - reads: 0 from the OS file cache, including disk I/O
  - dirtied: 0
  - writes: 0

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #345784 (closed)