Periodically clean up stale issues and pull requests (#1779)

Implements https://github.com/actions/stale to clean up PRs and issues that have been sitting for over 180 days without any sort of activity. Prompts users to rebase their PRs or bump their issues with interest.

This is the same action we use to keep our monorepo tidy

Author: austinpray-mixpanel

.github/workflows/stale.yaml

@@ -0,0 +1,34 @@
+name: Mark stale issues and pull requests
+
+on:
+  schedule:
+  - cron: '40 4 * * *'
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    permissions:
+      issues: write
+      pull-requests: write
+
+    steps:
+    # https://github.com/actions/stale
+    - uses: actions/stale@v5
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        days-before-stale: 180
+        days-before-close: 14
+        stale-issue-message: >
+          This issue has been inactive for over 180 days. It will be automatically closed in 14 days.
+          Label this issue as "never-stale" to exempt it from this check.
+
+          —[Mark stale](https://github.com/mixpanel/docs/actions/workflows/stale.yaml)
+        stale-pr-message: >
+          This PR has been inactive for over 180 days. It will be automatically closed in 14 days.
+          Label this PR as "never-stale" to exempt it from this check.
+
+          —[Mark stale](https://github.com/mixpanel/docs/actions/workflows/stale.yaml)
+        stale-issue-label: 'stale'
+        stale-pr-label: 'stale'
+        exempt-pr-labels: never-stale