chart: Add comment about Alertmanager confiration rendering with helm…

… template engine

Using the helm template engine with Alertmanager configurations
(Alertmanager.yaml) does not seem to work as expected.
It looks like the helm template engine does not recognise any
new config values since all configuration use cases are not
templated.

We resolve to creating a new secret which will be used to override
the default values making it possible for users to edit the
configuration settings.

Closes: #2262

charts/prometheus-operator.yaml

@@ -38,6 +38,19 @@ alertmanager:
             matchLabels:
               app.kubernetes.io/name: prometheus-operator-alertmanager
 
+  ## Passing the below configuration directives through the helm template
+  ## engine leads to no changes.
+  ## So let us create a new secret that overrides/patches
+  ## alertmanager-prometheus-operator-alertmanager secret with new config
+  ## read from a ConfigMap (metalk8s-alertmanager-config)
+  ## This implies we don't have to worry about patching the local charts
+
+  # config:
+  #   global: '__var_tojson__(alertmanager.spec.notification.config.global)'
+  #   templates: '__var_tojson__(alertmanager.spec.notification.config.templates)'
+  #   route: '__var_tojson__(alertmanager.spec.notification.config.route)'
+  #   receivers: '__var_tojson__(alertmanager.spec.notification.config.receivers)'
+  #   inhibit_rules: '__var_tojson__(alertmanager.spec.notification.config.inhibit_rules)'
 
 prometheusOperator:
   tlsProxy: