Add cron worker to automatically rollout zoekt exact code search to paid namespaces

What does this MR do and why?

Duo summary:

This merge request introduces a new Zoekt rollout system for search functionality. It adds a planning service to determine how to distribute search indices across available nodes, a provisioning service to execute the planned changes, and a rollout service to orchestrate the entire process. The changes also include a new worker to periodically run the rollout process, along with associated configuration and feature flag settings. Additionally, there are minor adjustments to existing models and scopes to support these new features. Overall, this update aims to improve the management and distribution of search indices across the system's infrastructure.

This is all behind the feature flag zoekt_rollout_worker

References

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• #508836

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ee/app/models/search/zoekt/enabled_namespace.rb

@@ -30,10 +30,6 @@ class EnabledNamespace < ApplicationRecord
         raw_sql = 'min(zoekt_indices.state) = :state AND max(zoekt_indices.state) = :state'
         joins(:indices).group(:id).having(raw_sql, state: Search::Zoekt::Index.states[:ready])
       end
-      scope :pending_assignment, -> {
-        joins(:namespace).merge(Project.all_projects.with_statistics).distinct
-        .where("metadata->>'complete' IS NULL OR metadata->>'complete' = 'false'")
-      }
 
       validates :metadata, json_schema: { filename: 'zoekt_enabled_namespaces_metadata' }
 
@@ -69,16 +65,6 @@ def update_last_used_storage_bytes!
         update_column(:metadata, metadata.merge(last_used_storage_bytes: size))
       end
 
-      def fetch_unassigned_projects(batch_size)
-        # Fetch all projects in the namespace that are not associated with any zoekt index
-        namespace.all_projects
-                 .with_statistics
-                 .left_joins(:zoekt_repositories) # Join with zoekt_repository, allowing NULL matches
-                 .where(zoekt_repositories: { id: nil }) # Filter for projects without a zoekt repository
-                 .joins(:statistics).order(repository_size: :desc) # Prioritize by repository size
-                 .limit(batch_size) # Limit the results to the batch size
-      end
-
       private
 
       def only_root_namespaces_can_be_indexed