Development: Add GitHub bot to mark pull requests as stale (ls1intu…

…m#5521)

.github/workflows/pullrequest-stale.yml

@@ -0,0 +1,25 @@
+name: Stale
+on:
+  schedule:
+    - cron: "0 12 * * *"
+
+jobs:
+  stale:
+    if: github.repository_owner == 'ls1intum'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check for stale PRs
+        uses: actions/stale@v5
+        with:
+          days-before-stale: 7
+          days-before-close: 14
+          # Disable issue checking, only PR
+          days-before-issue-stale: -1
+          remove-stale-when-updated: true
+          stale-pr-label: "stale"
+          exempt-pr-labels: "no-stale"
+          stale-pr-message: >
+            There hasn't been any activity on this pull request recently. 
+            Therefore, this pull request has been automatically marked as stale
+            and will be closed if no further activity occurs within **seven** days.
+            Thank you for your contributions.

docs/dev/guidelines/development-process.rst

@@ -96,3 +96,17 @@ Iterate steps 3 & 4 until ready for merge (all reviewers approve (thumbs up))
 --------
 A project maintainer merges your changes into the ``develop`` branch.
 
+
+
+Stale Bot
+=========
+
+If the pull request doesn't have any activity for at least 7 days, the stale bot will mark the PR as `stale`.
+The `stale` status can simply be removed by adding a comment or a commit to the PR. 
+After the PR is marked as `stale`, the bot waits another 14 days until the PR will be closed (21 days in total).
+Adding activity to the PR will remove the `stale` label again and reset the stale timer. 
+To prevent the bot from adding the `stale` label to the PR in the first place, the `no-stale` label can be used.
+This label should only be utilized if the PR is blocked by another PR or the PR needs help from another developer. 
+
+A full documentation on this bit can be found here:
+https://github.com/actions/stale