Fix Rubocop offenses for migration update mappings helper

.rubocop_todo/gitlab/bounded_contexts.yml

.rubocop_todo/search/namespaced_class.yml

...evelopment/search/advanced_search_migration_styleguide.md

...kers/concerns/elastic/migration_update_mappings_helper.rb

...ncerns/search/elastic/migration_update_mappings_helper.rb

...migrate/20231130152447_add_work_item_type_id_to_issues.rb

...ic/migrate/20240130154724_add_fields_to_projects_index.rb

...ic/migrate/20240208160152_add_count_fields_to_projects.rb

ee/elastic/migrate/20240410193847_add_embedding_to_issues.rb

ee/elastic/migrate/20240517092224_add_routing_to_issues.rb

...rate/20240626145458_add_root_namespace_id_to_work_item.rb

.../migrate/20240704125425_add_label_ids_to_merge_request.rb

...40814223217_add_issues_access_level_in_work_item_index.rb

...tic/migrate/20241003142503_add_embedding_to_work_items.rb

ee/elastic/migrate/20241003151804_add_notes_to_work_items.rb

...c/migrate/20241105111645_add_work_item_type_correct_id.rb

...ate/20241107131942_add_traversal_ids_to_merge_requests.rb

...migrate/20241204115350_add_assignees_to_merge_requests.rb

ee/spec/services/elastic/data_migration_service_spec.rb

...ures/migrations/elasticsearch/elasticsearch_migration.txt