Add and Configure Stale Bot

We have been received some amount of PRs where the authors are not very responsive.

I propose we add and configure [stale bot](https://github.com/actions/stale) and make some rule like marking it as stale within 2 weeks and closing with 4 weeks, so we don't have a lot of stale PRs on the line for review.

I know sometimes it'll apply for ourselves 😅 but maybe it's not bad that the bot will remind us!

Start with the linked actions/stale documentation and the repository's GitHub Actions configuration. Configure pull requests to be marked stale after two weeks and closed after four weeks, then verify that the workflow has the intended scope and timing.

Written by the indexing model from the issue text.