Refactor Alembic upgrade command in Jenkinsfile for improved execution

- Updated the Alembic upgrade command to use a Python script for execution, addressing issues with configuration handling in Docker.
- Enhanced comments to clarify the purpose of the changes and their implications for E2E testing.

Jenkinsfile

@@ -284,9 +284,8 @@ pipeline {
             e2e_compose_fail_logs
             exit 1
           fi
-          # Binario /usr/local/bin/alembic: sin python3 -m (el -c rompe; log con -c = build sin el último commit)
-          # --config=/ruta evita un token que empiece con - (algunos compose run lo mezclan con sus flags)
-          if ! e2e_compose run --rm --no-deps --entrypoint /usr/local/bin/alembic backend --config=/app/alembic.ini upgrade head; then
+          # e2e_alembic_upgrade.py: carga /app/alembic.ini en la API; la CLI a veces queda con config vacío bajo compose (No 'script_location')
+          if ! e2e_compose run --rm --no-deps --entrypoint /usr/local/bin/python3 backend /app/e2e_alembic_upgrade.py; then
             echo "ERROR: falló alembic upgrade head (job previo al stack completo)"
             e2e_compose_fail_logs
             exit 1