Zoekt: Add callback service

What does this MR do and why?

Add a service Search::Zoekt::CallbackService to process the callbacks from Zoekt.

When there is a delete task then it will destroy the zoekt_repository, if there is any indexing task then it will set indexed_at in the zoekt_repository. In addition to that it will move the task to done. For failures callbacks it will reduce the retry_count everytime. And finally when all the retries are exhausted it will move the task to failed.

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Before	After

How to set up and validate locally

Query plan

UPDATE
    "zoekt_tasks"
SET
    "updated_at" = '2024-05-14 17:01:55.654473',
    "state" = 255,
    "retries_left" = 0
WHERE
    "zoekt_tasks"."id" = 14

https://console.postgres.ai/shared/1abd8844-115e-4e46-b6d4-19bd03d02293

UPDATE
    "zoekt_repositories"
SET
    "updated_at" = '2024-05-14 17:05:36.919402',
    "indexed_at" = '2024-05-14 17:05:36.918149'
WHERE
    "zoekt_repositories"."id" = 15

https://console.postgres.ai/shared/d7ef40b5-69cd-4ecb-bee9-353acff564c8

DELETE FROM "zoekt_repositories"
WHERE "zoekt_repositories"."id" = 15

https://console.postgres.ai/shared/60464215-be68-4d97-aef6-e9c04ac4ea72

Related to #457202 (closed)