Update image source in releases page

This was causing an error with PDF generation as there was a potential chicken/egg issue as it could not reference an image in a remote location that did not exist yet.

Author: Jonathan S. Katz

docs/content/releases/4.5.0.md

@@ -30,7 +30,7 @@ PostgreSQL Operator is tested with Kubernetes 1.15 - 1.18, OpenShift 3.11+, Open
 
 ### [PostgreSQL Operator Monitoring](https://crunchydata.github.io/postgres-operator/latest/architecture/monitoring/)
 
-![PostgreSQL Operator Monitoring](https://crunchydata.github.io/postgres-operator/latest/images/postgresql-monitoring.png)
+![PostgreSQL Operator Monitoring](/images/postgresql-monitoring.png)
 
 This release makes several changes to the PostgreSQL Operator Monitoring solution, notably making it much easier to set up a turnkey PostgreSQL monitoring solution with the PostgreSQL Operator using the open source [pgMonitor](https://github.com/CrunchyData/pgmonitor) project.