Closes https://github.com/PostgREST/postgrest/issues/4107.
Adds two python scripts:
- monitor_pid.py: monitors the postgrest process each second
until it exits, then outputs a csv with the results. The nix wrappers
use the `loadtest` dir for the output.
- merge_monitor_result.py: receives a list of csvs and merges them into
a single markdown table. The nix wrappers use the `loadtest/*.csv`
files for the input.
The nix `postgrest-with-pgrst` and `postgrest-loadtest-report` commands
use these scripts to add monitoring for `postgrest-loadtest` and
`postgrest-loadtest-against`.
Wolfgang Walther