Update Changelog.md

Changelog.md

 # Changelog
 
+## [2.19] - 2024-10-09
+- LSO interaction rework: Skip a playbook automatically if the inventory is empty.
+- Introduction of LSOState type.
+- Celery: add as Executor, cleanup.
+- `promote_p_to_pe` and `update_ibgp_mesh`: add conditionals to distinguish between P and PE for the iBGP/SDP updates and PE-specific functions and logic.
+- Update of unit test in `test_update_ibgp_mesh`.
+
 ## [2.18] - 2024-10-01
 -  Use solo pool for Celery workers