Add golangci-lint GitHub Action

Created by: tsenart

This PR adds a GitHub Action that runs golangci-lint and reports results back as a PR review using reviewdog. The enabled linters are configured in the .golangci.yml file, so we can run locally the same thing during development if so wanted.

The enabled linters aren't set in stone, but I think are a useful initial choice — we can enable and disable some as we learn more about their usefulness with practice.

Review dog 🐶 will report any issues in any changed files, rather than only changed lines of code. I believe this is a good way for us to incrementally reduce these warnings, short of one big PR addressing them all. Please share your thoughts on this if you disagree.

Fixes #9193 (closed)