Provide a what-container pipe command to add a container column

Summary:
The command is intended to be used as a pipe:
ps auxw | grep bash | what-container

It parses stdin to append to the line the container name,
if it matches a pid launched in a container.

By default, pid is searched in the first two columns,
but a custom position can be given as argument:

ps auxw | grep bash | what-container -p 2

Ref T1456

Test Plan: Commands above

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1456

Differential Revision: https://devcentral.nasqueron.org/D1836