[FIX] web: number format in exported group header for float values

Exporting data incorrectly formats the float values of group headers

Steps to reproduce:
1. Install Planning
2. Open Planning and trigger the list view
3. Remove the default filter and add a group_by on employees
4. Export the data
5. The file produced doesn't have the same format for Allocated Hours in
   the group headers and in the line details

Solution:
Create formats for float and monetary values using the user's
preferences in decimal separator and decimal precision. For monetary
format, we use the biggest decimal precision used in the company
currencies.

opw-2864273

closes odoo/odoo#94534

Signed-off-by: Julien Castiaux <juc@odoo.com>