[FIX] web: calendar: fetch records in right timezone

Before this commit, the calendar searched records on the wrong time ranges
which did not take into account the timezone of the user
It obviously resulted in some records not being there

After this commit, all the relevant records are fetched according to the right
time range in UTC, corresponding to start/end of the week/month/day of the calendar

OPW 2076114

closes odoo/odoo#39240

X-original-commit: 70ed3d54
Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>