[URL drilldowns] provide better error messages for URL template parse failures

[nreese]

In the screen shot below, notice the parse failure message? The message would be much more helpful if it included the the available keys for the current trigger so instead of the error message below, how about something like "event.value is not available with range selection trigger. Try using event.from and event.to."

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesUx)

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)

[vadimkibana]

Discussing this with the team. We don't know of a good way to validate the errors, we don't have enough data to validate the drilldown Handlebars template at creation time. But we think the way present the Drilldown links in Dashboard better.