[APM] Preview alert thresholds

[nehaduggal]

Describe the feature:
Allow a user to preview how many times an alert would have triggered based on the threshold they set.

Describe a specific use case for the feature:
Our current alert experience does not allow a user to view how many times an alert would be triggered for the configured threshold. This can lead to the user picking a very low threshold and a lot of alert noise. Adding a way to preview number of times they will be notified will allow a user to set an optimum threshold and appropriate action based on the alert activity.

For the first version we can have a very simple experience where we surface the results of the preview on the alert fly out.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[formgeist]

@nehaduggal This probably needs a corresponding design issue to show how we want to implement the preview?

[nehaduggal]

@formgeist as discussed we won't need a separate design issue for this. Lets borrow the design from the existing Metrics alert preview. Attaching a screenshot. We should allow the customer to preview the results for the last hour, day, week, month.

[sorenlouv]

Replaced by #77313