[Watcher+Kibana] Ability to create an alert from Kibana charts

[elasticmachine]

Original comment by @bohyun-e:

In Tahoe All Hands 2017, we talked about adding a feature to create an alert directly from Kibana charts. This is one of the highly asked features, and the main end-users are going to be more naive users who aren't familiar with coding or scripting.

There are two obvious paths here (and probably more)

1. Add an ability to create an alert directly from the chart. E.g. you could drag a line over the chart to a specific threshold and that will trigger the watcher creation at that value.

2. We can have a tighter integration from Kibana dashboards and visualizations so that the users aren't losing context if and when they want to create an alert. One approach might be to provide a link from the chart that will send users to the Watcher creation UI but this UI will be pre-filled with some information about the metric that the users want to create an alert on. (field, chart they were looking at, etc.)

[elasticmachine]

Original comment by @bohyun-e:

Being able to create an alert from the monitoring charts is another related request but leaving that one out for this issue.

[elasticmachine]

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

[timroes]

Closing in favor of #71560