Update db_upgrade.py to append osm to metric_name to be BWC

Change-Id: I8ed6497fe21a3db3ccf841795f8b92af1a95cc0b
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/installers/charm/osm-update-db-operator/src/db_upgrade.py b/installers/charm/osm-update-db-operator/src/db_upgrade.py
index 72eaa81..295ce87 100644
--- a/installers/charm/osm-update-db-operator/src/db_upgrade.py
+++ b/installers/charm/osm-update-db-operator/src/db_upgrade.py
@@ -136,6 +136,7 @@
                         for vdur in monitored_vdurs:
                             vdu_id = vdur["vdu-id-ref"]
                             metric_name = vnf_monitoring_param.get("performance-metric")
+                            metric_name = f"osm_{metric_name}"
                             vdu_name = vdur["name"]
                             vnf_member_index = vnfr["member-vnf-index-ref"]
                             scalein_threshold = scaling_criteria.get("scale-in-threshold")