Create automation for syncing common CI/test files

[russellb]

We have a lot of files we're duplicating between several repos that are the same, or could be the same. I would like to either identify or create some automation to minimize the burden of keeping improvements and fixes in sync across repos.

Some examples:

• GitHub workflow for running actionlint
• GitHub workflow for running markdown lint
• Makefile snippets for running common tools like actionlint, md-lint
• spellcheck custom dictionary
• configuration and workflows for python formatting and linting to retain common standards throughout the project

[russellb]

This looks like what I envisioned: https://github.com/marketplace/actions/repo-file-sync-action

It supports a PR workflow where changes are synced by posting PRs. I would want to use that approach so that every change runs through review and CI before merging the sync.

[russellb]

@nathan-weinberg just FYI since you've been working on establishing common CI jobs across repos. I think we could use this repo (dev-docs) as a central home for files that are shared among multiple repos, plus some automation to automatically submit PRs to sync changes to other repos.

[nathan-weinberg]

Relates to #12