Consider adding a stale bot for issues/PR's

[MichelZ]

There's a lot of old issues, even some PR's that haven't been touched in quite some time.
Consider adding a stale bot (https://github.com/actions/stale) so that issues that have no activity are closed automatically.

It's also helpful to get engagement on issues that still need attention

To be clear, for people who don't know stale bot, my proposal would be a workflow like this:

• After e.g. 180 days without ANY activity, an issue gets flagged as "Stale" by adding a Label, e.g. "Stale"
• The bot also adds a comment to the issue informing the subscribers of this fact, and what to do to "Unstale" the issue (e.g. just adding a comment)
• After another for example 7-14 days of absolutely no activity on the issue, it would get closed (of course with the ability to re-open it)