[FIX] calendar: ics file missing organizer property

Steps to reproduce:

  - In odoo, create an event "example" in the future with alice@outlook.com and add
    bob@outlook.com to the attendees
  - In the bob outlook account, there should be an ics file with the
    following email "Invitation to example"
  - Drag and drop the ics file into outlook calendar
  -> Bob is set as the organizer

Cause of the issue:

  The organizer property is missing from the ics file
  cf https://www.rfc-editor.org/rfc/rfc5545#section-3.6.1



opw-2841276

closes odoo/odoo#100426

Signed-off-by: Arnaud Joset <arj@odoo.com>