fix: update PostgreSQL secret key for Bitnami chart 12.1.5

The new Bitnami PostgreSQL chart version 12.1.5 uses 'password' as the
secret key instead of 'postgresql-password'. This change aligns the
DolphinScheduler Helm chart with the new Bitnami chart format.

This fix resolves the E2E-K8S test failure caused by the post-install
hook timing out when trying to read the PostgreSQL password from the
wrong secret key.

Author: zhan7236

deploy/kubernetes/dolphinscheduler/templates/_helpers.tpl

@@ -170,7 +170,7 @@ Create a database environment variables.
     secretKeyRef:
       {{- if .Values.postgresql.enabled }}
       name: {{ template "dolphinscheduler.postgresql.fullname" . }}
-      key: postgresql-password
+      key: password
       {{- else if .Values.mysql.enabled }}
       name: {{ template "dolphinscheduler.mysql.fullname" . }}
       key: mysql-password