Improve get_process_golang_version()

The function accepts a `psutil.Process` and reads its /proc/pid/exe. It is cached on a per-Process basis, but Processes replace often and we can do smarter caching based on modification time of the absolute path of `/proc/pid/exe` based on the mnt ancestor, so `/proc/{get_mnt_ns_ancestor(process)}/root/path/to/exe`.