move notification formatting to each of the integrations

[MagnusRef]

Is your feature request related to a problem? Please describe.

Hello

Currently as of writing the format of the message string returned in getNotificationMessage includes a static description of the related cluster plus the actual message(s).

healthcheck-manager/controllers/notification.go

Lines 248 to 270 in be3a33b

	func getNotificationMessage(clusterNamespace, clusterName string, clusterType libsveltosv1beta1.ClusterType,
	conditions []libsveltosv1beta1.Condition, logger logr.Logger) (string, bool) {
	passing := true
	message := fmt.Sprintf("cluster %s:%s/%s \n", clusterType, clusterNamespace, clusterName)
	for i := range conditions {
	c := &conditions[i]
	if c.Status != corev1.ConditionTrue {
	passing = false
	message += fmt.Sprintf("liveness check %q failing \n", c.Type)
	message += fmt.Sprintf("%s \n", c.Message)
	}
	}
	if passing {
	message += "all liveness checks are passing"
	logger.V(logs.LogDebug).Info("all liveness checks are passing")
	} else {
	logger.V(logs.LogDebug).Info("some of the liveness checks are not passing")
	}
	return message, passing
	}

This makes it rather difficult to implement custom formatting for each of the notification implementation. (e.g. Slack, Teams).

For example I would like in the future to propose changing the Teams notification to use a more rich format instead of the current bland messages.

Describe the solution you'd like

My suggestion would be to just return the message string without the fmt.Sprintf("cluster %s:%s/%s \n", clusterType, clusterNamespace, clusterName) prefix, and let each implementation choose how it should be shown.

This would make it more flexible for each of the notification integration to tailor how it should look, since they are quite different from each other and each of them have different features available.

Describe alternatives you've considered

Alternatively beside the original message string, you could also just return a list of the messages, so each integration can pick and choose between original format or a more free format. This would keep it more DRY, since Im guessing that most of the notifications integration will keep the original format.

Additional context

in #162 I hinted at this

Currently these Messages are quite simple, so it would be cool in the furture if you could get a more parsable return from getNotificationMessage(), as Teams adaptive cards have a lot of features like formatting.