Resolve "Linear Project#ancestors"

What does this MR do?

Project#ancestors (aliased to #ancestors_upto) uses ObjectHierarchy to make recursive calls. We can replace this method with the linear version from the Namespace model. In practice we've found the linear versions to be faster and less complicated for the database optimizer to work with.

SQL Changes

Click through to the postgres.ai links for actual IDs used.

Project#ancestors

New

SELECT "namespaces".* FROM "namespaces" WHERE "namespaces"."id" IN (22, 23, 24)

Time: 4.003 ms  
  - planning: 2.956 ms  
  - execution: 1.047 ms  
    - I/O read: 0.927 ms  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 6 (~48.00 KiB) from the buffer pool  
  - reads: 13 (~104.00 KiB) from the OS file cache, including disk I/O  
  - dirtied: 0  
  - writes: 0 

https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/5825/commands/19745

Old

WITH RECURSIVE "base_and_ancestors" AS (
  (
    SELECT 
      "namespaces".* 
    FROM 
      "namespaces" 
    WHERE 
      "namespaces"."type" = 'Group' 
      AND "namespaces"."id" = 24
  ) 
  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"

Namespace#ancestors with hierarchy_order

The "SELECT namespaces.*" wrapper was added to normalize the SELECT. Otherwise you can get mismatched column count errors with unions. Union queries are common when working with namespace hierarchies.

SELECT 
  "namespaces".* 
FROM 
  (
    SELECT 
      "namespaces".*, 
      ABS(
        3 - array_length(traversal_ids, 1)
      ) as depth 
    FROM 
      "namespaces" 
    WHERE 
      "namespaces"."id" IN (27, 28) 
    ORDER BY 
      "depth" DESC
  ) namespaces

Time: 4.275 ms  
  - planning: 3.130 ms  
  - execution: 1.145 ms  
    - I/O read: 0.964 ms  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 9 (~72.00 KiB) from the buffer pool  
  - reads: 13 (~104.00 KiB) from the OS file cache, including disk I/O  
  - dirtied: 0  
  - writes: 0 

https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/5836/commands/19748

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

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• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
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Related to #337719 (closed)