Revert "chore(deps): update ghcr.io/lesuisse/shelly-ht-action-prometheus docker tag to v0.3.1"

The new image version suddenly requires to use a passphrase for no
reason. The connection is plaintext anyway.

This reverts commit 7ca808d5.

apps/base/iot/shelly-ht-monitor.yaml

@@ -17,7 +17,7 @@ spec:
     spec:
       containers:
         - name: shelly-ht-monitor
-          image: ghcr.io/lesuisse/shelly-ht-action-prometheus:0.3.1
+          image: ghcr.io/lesuisse/shelly-ht-action-prometheus:0.2.0
           env:
             - name: SENSOR_PASSWORD
               valueFrom: