A hotfix to Metric Threshold alerts (https://github.com/elastic/kibana/pull/106947/files#diff-bb5393c086e685993db2ac415c87a6b39151e97c0c1785aaff95981e41aae780L79-L83) accidentally removed logic that was necessary for alert previews to generate multiple buckets of data.

All metric previews will only ever say, at most, There was 1 instance that satisfied the conditions of the alert.

We need to:

• Restore this logic while preserving the bugfix
• Add a test to guard against bucket lookback logic being removed again