Add reusable GitHub Actions workflows

[PetarStoev02]

Create reusable CI workflow templates for: TypeScript build+test, npm publish, ESLint check. Other repos reference these.

[github-actions]

This issue has had no activity in 60 days. Flagging stale.
If it's still relevant, comment or add it to a due-dated milestone within 30 days, otherwise it will be auto-closed.