chore: add stale and lock issue workflows

Mark as stale and close issues (to keep ourselves focused, and ensure
that the issue is still relevant today).

Lock old issues to force new issue being created, even if the problem
looks similar.

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>

.github/workflows/lock.yaml

@@ -0,0 +1,18 @@
+name: 'Lock old issues'
+
+on:
+  schedule:
+    - cron: '0 2 * * *'
+  workflow_dispatch:
+
+permissions:
+  issues: write
+
+jobs:
+  action:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v5
+        with:
+          issue-inactive-days: '60'
+          process-only: 'issues'

.github/workflows/stale.yaml

@@ -0,0 +1,22 @@
+name: 'Close stale issues and PRs'
+on:
+  schedule:
+    - cron: '30 1 * * *'
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          stale-issue-message: 'This issue is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 7 days.'
+          stale-pr-message: 'This PR is stale because it has been open 45 days with no activity.'
+          close-issue-message: 'This issue was closed because it has been stalled for 7 days with no activity.'
+          days-before-issue-stale: 180
+          days-before-pr-stale: 45
+          days-before-issue-close: 5
+          days-before-pr-close: -1 # never close PRs