[FIX] survey: better datetime picker & fix date format issues

Issue

    - Install Surveys & Website
    - Create a survey with a datetime question
    - Install Spanish lang & set it up on website as the only language
    - Surveys > Your survey > Test

    Traceback

Cause

    There is a format mismatch because of field_utils.format.datetime
    but it's needed for timezone offsets.

Solution

    Format the field_utils.format.datetime result's into
    the datetimepicker format.

    I re-organized this part because it was a bit confusing and
    it handles error now.

OPW-2167397

closes odoo/odoo#43912

X-original-commit: b368b1db4a998a2369185218fe19fb84874f77ab
Signed-off-by: Jason Van Malder (jvm) <jvm@odoo.com>