Linear traversal query for Namespace#ancestors [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

Adds linear traversal query for Namespace#ancestors which has better query performance over recursive CTEs. Refactored from !36025 (closed).

#324749 (closed)

Screenshots (strongly suggested)

Queries

Original query

https://console.postgres.ai/gitlab/gitlab-production-tunnel/sessions/3896/commands/13413

WITH RECURSIVE "base_and_ancestors" AS (
(
    SELECT
      "namespaces".*
    FROM
      "namespaces"
    WHERE
      "namespaces"."type" = 'Group'
      AND "namespaces"."id" = 1755573)
  UNION (
    SELECT
      "namespaces".*
    FROM
      "namespaces",
      "base_and_ancestors"
    WHERE
      "namespaces"."type" = 'Group'
      AND "namespaces"."id" = "base_and_ancestors"."parent_id"))
SELECT
  "namespaces".*
FROM
  "base_and_ancestors" AS "namespaces"

New query

https://postgres.ai/console/gitlab/gitlab-production-tunnel/sessions/3849/commands/13120

SELECT
  "namespaces".*
FROM
  "namespaces"
WHERE
  "namespaces"."id" IN (9970, 1755573)

New query with hierarchy order

https://postgres.ai/console/gitlab/gitlab-production-tunnel/sessions/3849/commands/13125

SELECT
  "namespaces".*,
  ABS(3 - array_length(traversal_ids, 1)) AS depth
FROM
  "namespaces"
WHERE
  "namespaces"."id" IN (9970, 1755573)
ORDER BY
  "depth" ASC

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