Zoekt Add initial_indexing task

What does this MR do and why?

Add a new task initial_indexing which will move all the pending zoekt indices to initializing with an intermediate state in_progress. in_progress state is the condition when the indexing worker has been called for a zoekt_index. Also added a new worker NamespaceInitialIndexingWorker which calls index_async for each project(also sub-projects) under a namespace iteratively. The zoekt_index will be moved to initializing when the zoekt_repositories count for a namespace is greater than or equal to all the projects(including subprojects) in a namespace.

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Query plan

SELECT
    COUNT(*)
FROM
    "projects"
WHERE
    "projects"."namespace_id" IN (
        SELECT
            namespaces.traversal_ids[array_length(namespaces.traversal_ids, 1)] AS id
        FROM
            "namespaces"
        WHERE
            "namespaces"."type" = 'Group'
            AND (traversal_ids @> ('{9970}')))

https://console.postgres.ai/shared/60088a5e-96e3-452b-ac2d-a71bfb131c3f

SELECT
    "projects"."id"
FROM
    "projects"
WHERE
    "projects"."namespace_id" = 9970

https://console.postgres.ai/shared/3a55e61a-1a6e-4ecf-9be0-d591fe992d98

SELECT
    "namespaces"."id"
FROM
    "namespaces"
WHERE
    "namespaces"."parent_id" = 9970
    AND "namespaces"."type" = 'Group'

https://console.postgres.ai/shared/c3a83379-444d-48e0-98fa-fd51b170078d

Related to #442883 (closed)