15.14.1.054-INDATA-255

refactor: Simplify PostgreSQL conf template sourcing

The source path for PostgreSQL configuration templates has been simplified.

Previously, underscores in `ext_item` were removed when constructing the template filename. This change removes that transformation, directly using `{{ ext_item }}.conf`. This implies that template files in `files/postgresql_config/conf.d/` now match the `ext_item` loop variables directly (e.g., `auto_explain.conf`).