[CAL-5185] Use slots not date-ranges for two weeks availability check

[CarinaWolli]

For CRM contact owner and fairness filtering, we check if there is any availability within the first two weeks. If the filtered users aren't available, we fallback to the original hosts.

Currently, we do this like that in slots/util.ts:

diff =
  aggregatedAvailability.length > 0 ? aggregatedAvailability[0].start.diff(twoWeeksFromNow, "day") : 1; // no aggregatedAvailability so we diff to +1

It checks if there are any date ranges starting in that time span. However, even though there is a date range, it doesn't mean that it's enough time for an available slot. Instead, we first need to calculate available slots and then check if there is a slot starting in the timespan.

_{From SyncLinear.com | CAL-5185}