Faster update of force_share_with_group_lock_on_descendants

What does this MR do?

With large hierarchies, an update of the namespaces.share_with_group_lock column through Namespace#force_share_with_group_lock_on_descendants is very slow and can time out for our larger customers.

This fix is to convert the Namespace#force_share_with_group_lock_on_descendants method to a linear version to improve update performance.

SQL Analysis

Note for confidentiality I've used 123 for the namespace ID below. Click the postgres.ai links below if you want to see the real ID.

Old

This query performance varies wildly. Results range between 3 seconds to over a minute.

UPDATE 
  "namespaces" 
SET 
  "share_with_group_lock" = TRUE 
WHERE 
  "namespaces"."id" IN (
    SELECT 
      "namespaces"."id" 
    FROM 
      "namespaces" 
    WHERE 
      (
        traversal_ids @> ('{123}')
      ) 
      AND "namespaces"."id" != 123
  )

Time: 48.659 s  
  - planning: 3.979 ms  
  - execution: 48.655 s  
    - I/O read: 46.146 s  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 424367 (~3.20 GiB) from the buffer pool  
  - reads: 54989 (~429.60 MiB) from the OS file cache, including disk I/O  
  - dirtied: 52093 (~407.00 MiB)  
  - writes: 10 (~80.00 KiB)  

https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/5638/commands/19260 https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/5638/commands/19282

New

This query is consistently around 5 seconds.

UPDATE 
  "namespaces" 
SET 
  "share_with_group_lock" = TRUE 
WHERE 
  (
    traversal_ids @> ('{123}')
  ) 
  AND "namespaces"."id" != 123

Time: 5.613 s  
  - planning: 3.196 ms  
  - execution: 5.610 s  
    - I/O read: 1.877 s  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 399789 (~3.10 GiB) from the buffer pool  
  - reads: 54749 (~427.70 MiB) from the OS file cache, including disk I/O  
  - dirtied: 52097 (~407.00 MiB)  
  - writes: 10 (~80.00 KiB)  

https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/5638/commands/19262

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #336468 (closed)