chore: PR approval reminder (#2132)

PR approval reminder

Signed-off-by: Michele Dolfi <dol@zurich.ibm.com>

.github/workflows/pr-reminders.yml

@@ -0,0 +1,55 @@
+name: PR Workflow Approval Reminder
+
+on:
+  # schedule:
+  #   - cron: "0 */6 * * *" # every 6 hours
+  workflow_dispatch:
+
+jobs:
+  check-prs:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check PRs blocked by workflow approval
+        id: filter
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const { data: pulls } = await github.rest.pulls.list({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              state: 'open'
+            });
+
+            let result = '';
+
+            for (const pr of pulls) {
+              const { data: runs } = await github.rest.actions.listWorkflowRunsForRepo({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                event: 'pull_request',
+                head_sha: pr.head.sha
+              });
+
+              const waitingRuns = runs.workflow_runs.filter(r => r.status === 'waiting');
+              if (waitingRuns.length > 0) {
+                const runNames = waitingRuns.map(r => r.name).join(', ');
+                result += `• **PR #${pr.number}**: [${pr.title}](${pr.html_url})  \n   ⏸️ Workflows: ${runNames}\n\n`;
+              }
+            }
+
+            let message;
+            if (result === '') {
+              message = '✅ No PRs are blocked by workflow approval right now.';
+            } else {
+              message = `🚦 **PRs waiting for maintainer approval to run workflows:**\n\n${result}`;
+            }
+
+            core.setOutput('message', message);
+
+      - name: Send message to Discord via webhook
+        run: |
+          payload=$(jq -n --arg content "${{ steps.filter.outputs.message }}" '{content: $content}')
+          curl -X POST -H "Content-Type: application/json" \
+            -d "$payload" \
+            ${{ secrets.PR_REMINDER_DISCORD_WEBHOOK }}