[CI] Add stale issues workflow

[LukeShortCloud]

No description provided.

[LukeShortCloud]

This workflow does the following:

• Runs once a week
• Checks for GitHub Issues that are 1 year or older without any replies
• If any are found, a "Stale" label is added to the issue. A message is also posted to warn that the issue is stale and will be closed soon
• If there are no updates for another 30 days, the issue is automatically closed
• We can add the label "long-term" to anything we care about keeping around
  • For example, issues like this we probably want to keep around: JIT for POWER? #242
  • We can also remove the "Stale" label which will keep it open for another year

You can read more about this official GitHub Action here: https://github.com/actions/stale

[ptitSeb]

Ok, let's try this.