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 (closed)

MR acceptance checklist

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Before	After

How to set up and validate locally

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ee/app/services/search/zoekt/planning_service.rb

@@ -17,7 +17,7 @@ def initialize(
       end
 
       def plan
-        namespace_plans = enabled_namespaces.map do |enabled_namespace|
+        all_plans = enabled_namespaces.map do |enabled_namespace|
           Plan.new(
             enabled_namespace: enabled_namespace,
             nodes: nodes,
@@ -25,9 +25,23 @@ def plan
           ).generate
         end
 
+        namespace_plans = []
+        failed_plans = []
+
+        all_plans.each do |p|
+          if p[:errors].present?
+            failed_plans << p
+          else
+            namespace_plans << p
+          end
+        end
+
+        successful_plans = all_plans.filter { |p| !p[:errors].present? }
+
         {
           total_required_storage_bytes: namespace_plans.sum { |plan| plan[:namespace_required_storage_bytes] },
-          namespaces: namespace_plans
+          namespaces: successful_plans,
+          failures: failed_plans
         }
       end
 
@@ -67,14 +81,18 @@ def initialize(
         end
 
         def generate
-          num_replicas.times { simulate_replica_plan }
+          if fetch_projects.exists?
+            num_replicas.times { simulate_replica_plan }
+          else
+            create_empty_replica
+          end
 
           {
             namespace_id: namespace.id,
             enabled_namespace_id: enabled_namespace.id,
             namespace_required_storage_bytes: calculate_namespace_storage,
             replicas: replica_plans,
-            errors: errors
+            errors: errors.uniq
           }
         end
 
@@ -100,12 +118,22 @@ def simulate_replica_plan
           add_replica_plan(replica_indices)
         end
 
+        def create_empty_replica
+          best_node = nodes.reject do |node|
+            @used_node_ids.include?(node[:id])
+          end.max_by { |node| node[:unclaimed_storage_bytes] }
+
+          if best_node
+            replica_indices = [simulate_index(best_node)]
+            add_replica_plan(replica_indices)
+            @used_node_ids.add(best_node[:id])
+          else
+            log_error(nil, :node_unavailable, "No nodes available to create an empty replica")
+          end
+        end
+
         def fetch_projects
-          namespace.all_projects
-                  .with_statistics
-                  .joins(:statistics)
-                  .group('projects.id, project_statistics.id, repository_size')
-                  .order('repository_size DESC, projects.id ASC')
+          namespace.all_projects.with_statistics
         end
 
         def assign_to_node(stats, replica_indices)
@@ -153,7 +181,7 @@ def simulate_index(node)
           {
             node_id: node[:id],
             projects: { project_id_from: nil, project_id_to: nil },
-            required_storage_bytes: 0,
+            required_storage_bytes: 1.kilobyte,
             max_storage_bytes: node[:unclaimed_storage_bytes]
           }
         end