[nrf noup] workflows: Add manifest PRs creation

Adding action to create manifest PRs automatically.

Signed-off-by: Kari Hamalainen <[email protected]>
(cherry picked from commit 37486f5)

Author: karhama

.github/workflows/manifest-PR.yml

@@ -0,0 +1,18 @@
+name: handle manifest PR
+on:
+  pull_request_target:
+    types: [opened, synchronize, closed]
+    branches:
+      - ncs-v3.1-branch
+
+
+jobs:
+  call-manifest-pr-action:
+    runs-on: ubuntu-latest
+    steps:
+      - name: handle manifest PR
+        uses: nrfconnect/action-manifest-pr@main
+        with:
+          token: ${{ secrets.NCS_GITHUB_TOKEN }}
+          manifest-pr-title-details: ${{ github.event.pull_request.title }}
+          base-branch: v3.1-branch