Add zoekt update_replica_states task

What does this MR do and why?

Adds a task that is run on an interval that will update Zoekt::Replica states depending on the state of their assigned indices.

Related to #467406 (closed) and &14188 (closed)

Query Plans

Finding ready replicas

SELECT "zoekt_replicas".* FROM "zoekt_replicas" INNER JOIN "zoekt_indices" "indices" ON "indices"."zoekt_replica_id" = "zoekt_replicas"."id" WHERE "zoekt_replicas"."state" = 0 AND "indices"."state" = 10 GROUP BY "zoekt_replicas"."id", "indices"."id" HAVING (count(indices.id) = (SELECT count(zi.id) FROM zoekt_indices zi WHERE zi.zoekt_replica_id = zoekt_replicas.id))

https://console.postgres.ai/gitlab/gitlab-production-main/sessions/29710/commands/92221

Time: 168.931 ms  
  - planning: 2.228 ms  
  - execution: 166.703 ms  
    - I/O read: 154.209 ms  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 4078 (~31.90 MiB) from the buffer pool  
  - reads: 203 (~1.60 MiB) from the OS file cache, including disk I/O  
  - dirtied: 6 (~48.00 KiB)  
  - writes: 0  

Finding non ready replicas

SELECT "zoekt_replicas".* FROM "zoekt_replicas" INNER JOIN "zoekt_indices" "indices" ON "indices"."zoekt_replica_id" = "zoekt_replicas"."id" WHERE "zoekt_replicas"."state" = 10 AND "indices"."state" != 10

https://postgres.ai/console/gitlab/gitlab-production-main/sessions/29710/commands/92222

Time: 2.818 ms  
  - planning: 1.946 ms  
  - execution: 0.872 ms  
    - I/O read: 0.765 ms  
    - I/O write: 0.000 ms  
  
Shared buffers:  
  - hits: 3 (~24.00 KiB) from the buffer pool  
  - reads: 1 (~8.00 KiB) from the OS file cache, including disk I/O  
  - dirtied: 0  
  - writes: 0  

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