[FIX] microsoft_calendar: fetch full description

Step to reproduce:
- Create a event in outlook with a long description
- Load the event in Odoo

Current Behaviour:
- Odoo use the body preview to get the event description
If the body is longer then, the description in Odoo is incomplete.

Behaviour after PR:
- Change fetch option to get description as text
- Use body['content']  as description which is the full body.

opw-2746358

closes odoo/odoo#84054

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