Set operator image tag to release v5.4.0

After pulling major-upgrades into postgres-operator, a new
image will be needed to install a fully functional operator.
This commit bumps the tag on the operator image to the
presently unreleased v5.4.0.

Issue: [sc-16349]

Author: tony-landreth

config/default/kustomization.yaml

@@ -11,4 +11,4 @@ bases:
 images:
 - name: postgres-operator
   newName: registry.developers.crunchydata.com/crunchydata/postgres-operator
-  newTag: ubi8-5.3.0-0
+  newTag: ubi8-5.4.0-0