Write task to migrate budget admins and valuators

If we didn't run this task, investments for existing budgets wouldn't
show their administrator/valuators as an option when we're editing them,
leading to data loss.

lib/tasks/migrations.rake

@@ -4,4 +4,17 @@ namespace :migrations do
     ApplicationLogger.new.info "Updating valuation taggings context"
     Tagging.where(context: "valuation").update_all(context: "valuation_tags")
   end
+
+  desc "Migrates budget staff"
+  task budget_admins_and_valuators: :environment do
+    ApplicationLogger.new.info "Updating budget administrators and valuators"
+    Budget.find_each do |budget|
+      investments = budget.investments.with_hidden
+
+      budget.update!(
+        administrator_ids: investments.where.not(administrator: nil).distinct.pluck(:administrator_id),
+        valuator_ids: Budget::ValuatorAssignment.where(investment: investments).distinct.pluck(:valuator_id)
+      )
+    end
+  end
 end