Add additional support for `RLIMIT` handling

[Pijukatel]

The measurement should take into consideration other limits that can be imposed through RLIMIT

For example, here the ulimit imposed limit is more restrictive than MemoryMax

ulimit -v 102400;systemd-run --user --scope --quiet --no-ask-password -p MemoryMax=150M -p MemorySwapMax=0 python3 sensor.py;

This must be done carefully, as those limits do not mean the same thing, but both should be taken into consideration when giving the maximum available memory