Add naming conventions to migration style guide

doc/development/migration_style_guide.md

@@ -114,6 +114,18 @@ rails schema statement: [`add_index`](https://api.rubyonrails.org/v5.2/classes/A
 This is a blocking operation, but it doesn't cause problems because the table is not yet used,
 and therefore it does not have any records yet.
 
+## Naming conventions
+
+We keep column names consistent with [ActiveRecord's schema conventions](https://guides.rubyonrails.org/active_record_basics.html#schema-conventions).
+
+Custom index names should follow the pattern `index_#{table_name}_on_#{column_1}_and_#{column_2}_#{condition}`.
+
+Examples:
+
+- `index_services_on_type_and_id_and_template_when_active`
+- `index_projects_on_id_service_desk_enabled`
+- `index_clusters_on_enabled_cluster_type_id_and_created_at`
+
 ## Heavy operations in a single transaction
 
 When using a single-transaction migration, a transaction holds a database connection