Add Spell Checker

[jgfoster]

@prestoncarman, Would you be able to do this?

[per1234]

I'm a big fan of codespell.

There is an official GitHub Actions action for it:
https://github.com/codespell-project/actions-codespell

We have been using it in the CI systems of Arduino's firmware and tooling repositories for the last few years with all good results. This is the standalone workflow we use in the firmware repos:
https://github.com/per1234/.github/blob/main/workflow-templates/spell-check.md

and this is the Task-based one we use in the tooling repos:
https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/spell-check-task.md