pid and mmap resource limits on ci-runner-x86-03-shadow

TLDR: Please bump pid_max, max_map_count, and max # of open files. Per https://shadow.github.io/docs/guide/system_configuration.html, the recommendations are 10M for # of open files, and 1B for max map count. We don't have a documented recommended max pid; my desktop has that set to 4M, which should be plenty.

Reason - I'm bumping into some more resource limits in larger simulations. (Increasing the number of clients in the simulation 100x for jnewsome/sponsor-61-sims#5 (closed)). This results in creating in the neighborhood of 200k processes.

It looks like the max # of pid's is ~81k - definitely too low. Likewise with max map count currently at 64k (shadow has several mmappings for each process in the simulation). The current max number of open files of 1M might be ok, but is a bit close for comfort given that every file open in every simulated process is actually opened in shadow, including stdout and stderr, so we're already looking at at least ~400k.

Current limits from https://gitlab.torproject.org/jnewsome/sponsor-61-sims/-/jobs/29436#L2951

cat /proc/sys/kernel/pid_max
+ tee /builds/jnewsome/sponsor-61-sims/jobs/tornet/sysinfo/pid_max
81920
+ cat /proc/sys/vm/max_map_count
+ tee /builds/jnewsome/sponsor-61-sims/jobs/tornet/sysinfo/max_map_count
65530
+ ulimit -a
open files                      (-n) 1048576