workflows: Create workflow to stale issues based on date

The standard stale/action is intended to be run regularly with
a date offset, but we want to have one we can run against a specific
date in order to run the stale bot against issues created since a particular
release milestone, so calculate the offset in one step and use it in the next.

At the moment we want to run this to stale issues before 9th October 2022 when Kata 3.0 was release, so default to this.

Note the stale action only processes a few issues at a time to avoid rate limiting, so why we want a cron job to it can get through
the backlog, but also to stale/unstale issues that are commented on.

.github/workflows/stale_issues.yaml

@@ -0,0 +1,41 @@
+name: 'Stale issues with activity before a fixed date'
+on:
+  schedule:
+    - cron: '0 0 * * *'
+  workflow_dispatch:
+    inputs:
+      date:
+        description: "Date of stale cut-off. All issues not updated since this date will be marked as stale. Format: YYYY-MM-DD e.g. 2022-10-09"
+        default: "2022-10-09"
+        required: false
+        type: string
+
+permissions: {}
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  stale:
+    name: stale
+    runs-on: ubuntu-24.04
+    permissions:
+      actions: write # Needed to manage caches for state persistence across runs
+      issues: write # Needed to add/remove labels, post comments, or close issues
+    steps:
+      - name: Calculate the age to stale
+        run: |
+          echo AGE=$(( ( $(date +%s) - $(date -d "${DATE:-2022-10-09}" +%s) ) / 86400 )) >> "$GITHUB_ENV"
+        env:
+          DATE: ${{ inputs.date }}
+
+
+      - name: Run the stale action
+        uses: actions/stale@5bef64f19d7facfb25b37b414482c7164d639639 # v9.1.0
+        with:
+          stale-pr-message: 'This issue has had no activity for at least ${AGE} days. Please comment on the issue, or it will be closed in 30 days'
+          days-before-pr-stale: -1
+          days-before-pr-close: -1
+          days-before-issue-stale: ${AGE}
+          days-before-issue-close: 30