…for day units (elastic#224083)

**Addresses:** elastic#223446

## Summary

This PR fixes an issue when time duration normalized to day(s) is shown as 0 seconds. The fix is performed by allowing using days time unit at rule schedule.

## Details

The issue happens when rule schedule's look-back gets normalized to day(s). The reason is that look-backs input doesn't support Days time unit. It leads to inability to parse the value and displaying the default value which is 0 seconds.

Rule schedule is shown to the users as rule `interval` and `look-back` while rule's SO saves the schedule by using three fields `interval`, `from` and `to`. Where `look-back` represents a logical value calculated as `lookback` = `to` - `from` - `interval`. Taking that into account it's becomes harder to maintain the original time duration unit value during prebuilt rules upgrade workflow (See elastic#204317 for more details).

The easiest way to fix this issue is to allow Days time unit in rule schedule inputs. On top of that 24 hours are always 1 day making hours the largest simply convertible time unit. The PR allows hours in rule schedule.

**Before:**

https://github.com/user-attachments/assets/4f2038f1-4a6a-4a88-b86e-381a5b717605

**After:**

https://github.com/user-attachments/assets/74875bf2-9341-425f-a35f-c8b088c1ef6a
(cherry picked from commit a013929)