Discovered in dotnet/runtime#63963, build https://dev.azure.com/dnceng/public/_build/results?buildId=1567505&view=results.

A test is being added which calls ps from command line. It works on most of the Linuxes we run the tests on a PR, but it seems to fail on mcr.microsoft.com/dotnet-buildtools/prereqs:debian-10-helix-amd64-20210304164434-56c6673 with:

System.ComponentModel.Win32Exception : An error occurred trying to start process 'ps' with working directory '/root/helix/work/workitem/e'. No such file or directory

As part of the PR, a check if ps is supported will be added, but @safern recommended to also add the command into our images.

Note that the command might be missing from more images depending on where we do and don't run tests during PRs.

I'm willing to put up a PR to add procps, I'd just need a bit help locating the right Dockerfiles. I'm also not sure if the change needs to be followed by a change in runtime repo.