Shellcheck integration

Context

We've started adding shell scripts under scripts/ for various purposes including utility, convenience, and usage in CI. We should make sure that these scripts are relatively portable and don't contain weird errors or bad practices.

Overview

Added a make job and pipeline integration for Shellcheck, a useful tool that finds all kinds of hidden issues in shell scripts. Should be fairly self-explanatory -- I based this off of Tyler's work integrating clang-format.

How was this tested?

Locally (Linux) and in the pipeline. It would be nice if a Mac user could test the make job too, although there really shouldn't be any reason it would fail as long as Shellcheck is installed.