Originally the starting dates for the new governing bodies for the new
legislature was set to `2025-01-01` for all relevant municipalities, OCMWs,
districts, and provinces.
These migrations change that to more correct starting dates:
* For organisations that are **not** involved in mergers the new starting data
is `2024-12-02`, the first day installation meetings are allowed[1].
* For organisations that are involved in mergers the new starting date is
`2025-01-01`, the first work day of the new year on which the mergers take
effect. Note: this migration assumes there are no other start dates on
`2025-01-01`, so the migrations have to be run in the specified order.
[1] https://www.vlaanderen.be/lokaal-bestuur/organisatie-en-werking/gemeenteraad/installatie
b1cc9c7329