Update memory limit configuration in Docker setup for DOMserver

[hqy2000]

Description:
We encountered a crash caused by an excessive number of clarifications, resulting in the jury page consuming too much memory to load. The error log indicated that the server was unable to allocate more than 512 MB of memory.

Steps to reproduce:

1. Use the DOMjudge Docker image (8.2.3). Note: the memory issue seems to be better in 8.3.0.
2. Generate a large number of clarifications in the system.
3. Attempt to load the jury page.

Observed behavior:
The server crashes due to insufficient memory allocation.

Root cause:

• Inside configure.sh, the memory limit in php.ini is set to memory_limit = 2G.
• However, the domserver overrides this limit by defining its own memory limit in domjudge-fpm.conf, which is set to 512 MB. This setting is unrelated to the one in php.ini.

Workaround:
I was able to resolve the issue by updating the memory limit in domjudge-fpm.conf to a higher value.

Proposed solution:
Update the Docker setup script to modify the domjudge-fpm.conf memory limit automatically during the configuration process, ensuring it aligns with the desired memory limit (e.g., 2G as set in php.ini).

[nickygerritsen]

Best would be if we can make this into an environment variable I think.