add support for autolabel stale PR (#1075)

* add support for autolabel stale PR

automatically labels stale PRs

* stale label is kind/stale

updates the stale label to reflect
existing project labels

* adds a relevant stale message

for both PRs and issues there is now a more
descriptive and relevant message
when the action marks something stale

* no auto-close on stale issues/prs

uses the exempt flag to ignore issues already marked
stale. this will allow us to auto label stale,
and then ignore them so they do not get auto
closed.

.github/workflows/stale.yml

@@ -0,0 +1,21 @@
+name: Mark stale issues and pull requests
+
+on:
+  schedule:
+  - cron: "0 0 * * *"
+
+jobs:
+  stale:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/stale@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-issue-message: 'This issue is being marked as stale due to a long period of inactivity'
+        stale-pr-message: 'This PR is being marked as stale due to a long period of inactivity'
+        stale-issue-label: 'kind/stale'
+        stale-pr-label: 'kind/stale'
+        exempt-issue-label: 'kind/stale'
+        exempt-pr-label: 'kind/stale'