Timeout exceptions in Zoekt::PlanningService during rollout

Background

We are iterating over all projects of a root namespace using all_projects. This is getting timeout.

Proposal

Use the approach similar to this https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/workers/search/zoekt/initial_indexing_event_worker.rb?ref_type=heads#L55-69 to iterate over all projects. This is iterating of ProjectNamespace in batches. That means we need to add project_namespace_ids in the Index metadata

Scope of this issue should be to just add project_namespace_id_from and project_namespace_id_to in the zoekt_indices.metadata column. Filling of these values will be done via #508836 (closed)