Replica search is not respecting the search field of enabled_namespace

What does this MR do and why?

Change the scope for_namespace to for_root_namespace_id_with_search_enabled. This new scope will also check the search: true

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Before	After

How to set up and validate locally

• Set up Zoekt for a namespace.
• Enable the FF zoekt_search_with_replica.
• Set the search field in the zoekt_enabled_namespace to false
• Now perform a group level search in this namespace. It should not use Zoekt

Query

SELECT
    1 AS one
FROM
    "zoekt_replicas"
    INNER JOIN "zoekt_enabled_namespaces" "zoekt_enabled_namespace" ON "zoekt_enabled_namespace"."id" = "zoekt_replicas"."zoekt_enabled_namespace_id"
WHERE
    "zoekt_enabled_namespace"."search" = TRUE
    AND "zoekt_replicas"."namespace_id" = 9970
    AND "zoekt_replicas"."state" = 10
LIMIT 1

https://console.postgres.ai/shared/3fae56e9-7105-448e-966f-5ebaef18e41d

Related to #479328 (closed)