[FIX] resource: week_type for new periods

In a calendar with 2 weeks mode (odd and even), before this commit, all
new created periods (placed in one of the two sections) don't have the
week_type field set. This generates a confusion, because a period that
should be applied only in odd weeks, for instance, it was applied also
in the even weeks.

Now, the new periods will have the week_type field set with the
week_type of the section where is it. Also, an error message is raised
if a period is not in one of the two sections.

opw-2239966

closes odoo/odoo#50393

Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>