Upgrade to symfony 6.4 and php 8.4

[baszoetekouw]

(continues from #1799)

Goal is to upgrade Engineblock to a recent version (6.4) of Symfony and supported version of php (8.4).

Symfony 5.4 --> 6.4
php 8.2 --> php 8.4

For each fo the steps to be finished, we need the following

all tests (behat and cypress) green
all deprecations fixed
Changelog.md updated with instructions on how do do the upgrade (e.g.., how to update config files)

Each of the separate steps is a subticket below.
If a step is finished, it is merged to the upgrade branch. After all steps are done, we will perform a performance test and and acceptance test in SURFconext (to be determined that that means exactly).

Together with the engineblock/upgrade branch, there is a devconf branch that contains the needed changes in devconf:
OpenConext/OpenConext-devconf#55

This work is carried out by Ibuildings/SURF en Kennisnet. Alternatingly, one of the two is in the lead, as indicated above, while te other provides support.