Updated community installer to use grafana 8.1.1 and prometheus v2.28.1

Change-Id: If64a82ccd300a512e69156101ee413377aaa8f1b
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/installers/docker/osm_pods/prometheus.yaml b/installers/docker/osm_pods/prometheus.yaml
index 2b2ee5f..adf3c11 100644
--- a/installers/docker/osm_pods/prometheus.yaml
+++ b/installers/docker/osm_pods/prometheus.yaml
@@ -93,7 +93,7 @@
             mountPath: /etc/prometheus_init
       containers:
       - name: prometheus
-        image: prom/prometheus:v2.4.3
+        image: prom/prometheus:v2.28.1
         args:
         - --config.file=/etc/prometheus/prometheus.yml
         - --web.enable-lifecycle