ZTC-3215: Add pause syscall to seccomp SERVICE_BASICS allowlist

[OmegaJak]

std::process::exit() has a safeguard on linux against libc::exit thread unsafety which will pause a thread if it tried to exit simultaneously with another thread. This pause uses the pause syscall.

If this race condition is triggered with the default seccomp configuration, the process will be killed by seccomp. This has been observed in a production environment.

This PR adds the pause syscall to the default seccomp allowlist to avoid this issue.

I don't think this poses any meaningful additional security risk by allowing potential malicious code to invoke it - at most, it can suspend a thread indefinitely, which I believe could already be accomplished with the futex syscall, which is already in the RUST_BASICS allowlist.

[OmegaJak]

It seems glibc pause is implemented using ppoll instead on aarch64: https://codebrowser.dev/glibc/glibc/sysdeps/unix/sysv/linux/pause.c.html#31
https://codebrowser.dev/glibc/glibc/sysdeps/unix/sysv/linux/aarch64/arch-syscall.h.html

So I've added the relevant #[cfg] to allow ppoll with those specific arguments on aarch64