scripts: Introduce benchmark_memory_usage.sh

scripts: Introduce benchmark_memory_usage.sh

Add shell script to sample PulseAudio memory usage while increasing
the number of connected 'paplay' clients over time.

Linux kernel /proc/$PID/smaps Private and Shared_Dirty fields are used
to accurately measure the total size of used dirty pages over time.
This shall be useful for benchmarking the PA daemon's memory while
introducing new features like per-client SHM access and memfds.

Also add an empty benchmarks-collection directory 'benchmarks/'. All
output from the benchmarking tools shall be saved in this place, with
timestamps and symbolic links to the newest versions.

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>