[O11y][PostgreSQL] Lens migration for Database Overview visualizations to Kibana version 8.4.0 (#5748)

* Migrate Database Overview dashboard visualizations to lens

* Update changelog

* Update screenshot

* Update Y-axis label for Local and shared block cache stats

Author: rajvi-patel-22

packages/postgresql/changelog.yml

@@ -1,4 +1,9 @@
 # newer versions go on top
+- version: "1.12.0"
+  changes:
+    - description: Migrate `Database Overview` dashboard visualizations to lens.
+      type: enhancement
+      link: https://github.com/elastic/integrations/pull/5748
 - version: "1.11.0"
   changes:
     - description: Migrate `Overview` dashboard visualizations to lens.