Automatically close stale issues and PRs

Issues and PRs with no activity after 10 months should be closed as stale.

Making use of the [close-stale-issues](https://github.com/marketplace/actions/close-stale-issues) action, we can add a stale label after a given time to warn relevant contributors that the issue will soon be closed automatically.

Start by reading the linked close-stale-issues action documentation and checking the repository's GitHub Actions configuration. Configure the action to warn about issues and pull requests after 10 months of inactivity, then close them automatically after the warning period; done means the workflow is present and its timing matches the issue request.

Written by the indexing model from the issue text.