Symfony/php upgrade voor Engineblock #1799

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

We will do this is multiple steps:

• Symfony 3.4 --> 4.4 (kennisnet)
• Symfony 4.4 --> 5.4 (ibuildings)
• php 7.2 --> php 8.2 (ibuildings)
• 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 carries out by Ibuildings/SURF en Kennisnet. Alternatingly, one of the two is in the lead, as indicated above, while te other provides support.