[AO] Extract into a package alerts summary time-range utilities

[tonyghiani]

📓 Summary

With the implementation of the AlertSummary component in #149579, it would be better to move these utilities to a package and then use them in both the observability and infra plugins:

• calculateTimeRangeBucketSize
• getAlertSummaryTimeRange
• useTimeBuckets

✔️ Acceptance criteria

• The calculateTimeRangeBucketSize utility should keep the same API signature to facilitate its abstraction
• The getAlertSummaryTimeRange utility should keep the same API signature to facilitate its abstraction
• The useTimeBuckets utility should keep the same API signature to facilitate its abstraction
• All the related tests and dependencies (constants, other utilities) should be extracted as well.

👨‍💻 Implementation hints

Over the extraction of these utilities, we could export an additional custom hook that organizes the usage of these utilities and provide a ready-to-use custom hook to retrieve the alerts summary time range, something like this:

const useSummaryTimeRange = (timeRange: TimeRange) => {
  const timeBuckets = useTimeBuckets();

  const bucketSize = useMemo(
    () => calculateTimeRangeBucketSize(unifiedSearchDateRange, timeRange),
    [timeRange, timeBuckets]
  );

  return getAlertSummaryTimeRange(
    timeRange,
    bucketSize?.intervalString || DEFAULT_INTERVAL,
    bucketSize?.dateFormat || DEFAULT_DATE_FORMAT
  );
};

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)