Fix prometheus tests

For chart testing the prometheus operator started to require (from 63.0.0
version) label release that equal to `prometheus` in the default deployment done
in our CI.

The change from the upstream:
prometheus-community/helm-charts#4818

Author: RafalKorepta

charts/redpanda/ci/14-prometheus-no-tls-values.yaml

@@ -18,3 +18,5 @@ tls:
 
 monitoring:
   enabled: true
+  labels:
+    release: prometheus

charts/redpanda/ci/15-prometheus-tls-values.yaml

@@ -18,3 +18,5 @@ tls:
 
 monitoring:
   enabled: true
+  labels:
+    release: prometheus

charts/redpanda/testdata/template-cases.golden.txtar

@@ -19720,6 +19720,7 @@ metadata:
     app.kubernetes.io/managed-by: Helm
     app.kubernetes.io/name: redpanda
     helm.sh/chart: redpanda-5.9.5
+    release: prometheus
   name: redpanda
   namespace: default
 spec:
@@ -21147,6 +21148,7 @@ metadata:
     app.kubernetes.io/managed-by: Helm
     app.kubernetes.io/name: redpanda
     helm.sh/chart: redpanda-5.9.5
+    release: prometheus
   name: redpanda
   namespace: default
 spec: