time_picker: Reduce increment of minutes to one.

After some discussions in CZO, it was decided that we should reduce the
increment of minutes to one because the up/down arrow isn't very helpful
at all. Most of the time, users would manual type their desired time and
micro adjust with the arrow keys if needed.

This change also solves the issue where the time picker only counts
multiples of 5s as valid time as it was tied to the increment of minutes.

web/src/flatpickr.js

@@ -30,6 +30,7 @@ export function show_flatpickr(element, callback, default_timestamp, options = {
         formatDate: (date) => formatISO(date),
         disableMobile: true,
         time_24hr: user_settings.twenty_four_hour_time,
+        minuteIncrement: 1,
         onKeyDown(selectedDates, dateStr, instance, event) {
             // See also the keydown handler below.
             //