for repeat_type = 'forever' recurrences.

Consider a recurrence creating a task every 15th day of the month.
When the cron runs, it updates the next recurrence dates of the
recurrence.

But currently, the updated "next_recurrence_date" can be set to an
earlier date than today, if the fixed day of the recurring task is
earlier than the current day.

This means that the recurring task to create every 15th of the month
will be created the 15, the 16, the 17, the 18, ... until the next month
begins (no task will be created when the cron runs before the 15th of a
month).

This commit enforces the next recurrence_date to be set after the
current cron run, to ensure a task isn't wrongly created multiple times.

This commit also includes the tests that led to the discovery of this
bug.

closes odoo/odoo#63518

Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

For recurrences of repeat_type = 'after', the daily cron would create 
tasks infinitely.

* The cron creates recurring task for all recurrences for which 
next_recurrence_date < today.
* next_recurrence_date was never updated.

This commit ensures that next_recurrence_date is set to False for 
repeat_type = 'after' recurrences, when the last recurrence is created.

Some interventions are done on a regular basis (e.g. maintenance of
fire alarms, safety inspections). Having tasks auto-generate would
facilitate the process and would ensure that the next intervention
isn't missed/forgotten.

closes odoo/odoo#55517

Taskid: 2172156
Related: odoo/enterprise#12246
Related: odoo/upgrade#1604
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>