[FEATURE] Document content of ctx for better message composition

[tarjei]

Is your feature request related to a problem?

When I am creating an alert message, I want the message to contain as much information as possible, but I do not know the structure of the ctx element and what it contains.

What solution would you like?
A dump of a sample ctx object from the query I am alerting on.

What alternatives have you considered?
A link to a document that explains the structure of the ctx document.

Do you have any additional context?

This screenshot shows the problem: OK I get a link to mustache templates, but that isn't of much help!