Enable automatically marking stale issues

[surajssd]

Right now we don't have a way to prune old issues from the repo. So a lot of issues stay stale and lingering around. I suggest that we enable bot so that the original authors can adjust issues on stale issues if things have changed / progressed in the project.

One way to do it is: https://github.com/actions/stale but if there is a bot that can do that for us, we can use that too.