Disables direct connection model is pinned

What does this MR do and why?

Disables direct connection model is pinned

If customers pin a model for completion, the IDEs have currently no way of fetching that model info for requests. As a contigency, we follow a simillar approach to other simillar scenarios by disabling direct connections to AIGW for completion. This MR is to be reverted once #541382 is complete

Database

SELECT
    1 AS one
FROM
    "ai_namespace_feature_settings"
WHERE
    "ai_namespace_feature_settings"."namespace_id" IN (1, 2)
    AND NOT ("ai_namespace_feature_settings"."offered_model_ref" = ''
            OR "ai_namespace_feature_settings"."offered_model_ref" IS NULL)
    AND "ai_namespace_feature_settings"."feature" = 1
LIMIT 1

https://console.postgres.ai/gitlab/gitlab-production-main/sessions/40226/commands/123820

MR acceptance checklist

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Related to #542826 (closed)