Update to the latest GitHub actions and workflows @aknysh (#39)

what

• Update to the latest GitHub actions and workflows

why

• Standardization
• Use the latest GitHub actions and workflows in all the consecutive PRs for testing and linting

Add `slash-command-dispatch` GitHub Actions workflow @maximmi (#32)

what

• Add slash-command-dispatch GitHub Actions workflow

why

• In a repo with the GitHub actions workflow present, when a PR is opened, we can comment on the PR with commands /build-readme and /terraform-fmt to rebuild README and format terraform code and push the changes back to the PR repo