[Alerting] provide links to Kibana alerting as context variables for alerting actions

[pmuellr]

Along with all the other mustache template variables we provide for action parameters, we should provide a link to the Kibana details page for the alert, and probably a link to the Kibana alert management page, which a customer could then add to the messages in their actions.

Here's what we currently make available:

kibana/x-pack/plugins/alerting/server/task_runner/transform_action_params.ts

Lines 38 to 46 in e1d787a

	const variables = {
	alertId,
	alertName,
	spaceId,
	tags,
	alertInstanceId,
	context,
	state,
	};

This implies we can get an external link to Kibana, and then once we have that, hopefully creating a URL based on that should be easy:

eg

• ${kbn-url}/app/kibana#/management/kibana/triggersActions/alert/${alert-id}
• ${kbn-url}/app/kibana#/management/kibana/triggersActions/alerts

We should then add one of these links to the default message from the index threshold:

kibana/x-pack/plugins/alerting_builtins/server/alert_types/index_threshold/action_context.ts

Lines 52 to 66 in 9ad8b8f

	const message = i18n.translate(
	'xpack.alertingBuiltins.indexThreshold.alertTypeContextMessageDescription',
	{
	defaultMessage:
	'alert {name} group {group} value {value} exceeded threshold {function} over {window} on {date}',
	values: {
	name: alertInfo.name,
	group: baseContext.group,
	value: baseContext.value,
	function: humanFn,
	window,
	date: baseContext.date,
	},
	}
	);

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[pmuellr]

DUP of #49392