[Migration][Metric threshold] Add an option in UI to suggest updating from metric threshold to custom threshold

[maryam-saeidi]

Summary

This ticket is about adding a suggestion button to the UI to allow users to migrate their rule from the metric threshold to the custom threshold.
@fkanout had an on-week about this topic, and this flow will look something like this:

Screen.Recording.2024-03-04.at.17.19.13.mov

Questions

1. How do we want to handle the warning threshold?
   For the first step, we can ignore the warning threshold since this is a suggestion. In the future, we can possibly ask the user whether they want to create a warning alert or an actual alert. (With the current setup, we have an issue with sending the recovered action of a warning rule to the correct channel that made our users separate warning vs alert rules to get the right notification)
2. Do we want to delete the original rule? No. Since it is a suggestion, it would be better to keep the original rule in case the user wanted to delete it later on.
3. How would the UI look like? Needs @maciejforcone 's input.
4. How can we gather information about how many people actually used this flow?

AC

• Implement a migration option from Metric threshold to Custom threshold via UI

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)