chore: add notification action

[skip ci]

.github/workflows/notify_pr.yaml

@@ -0,0 +1,22 @@
+name: Notify Google Chat on new PR
+
+on:
+  pull_request:
+    types:
+      - opened
+
+jobs:
+  notify-pr-google-chat:
+    runs-on: docker
+    container:
+      image: alpine:latest
+    steps:
+      - name: Notify
+        uses: ./.github/actions/notify
+        with:
+          title: New Pull Request
+          event_title: ${{ github.event.pull_request.title }}
+          event_author: ${{ github.event.pull_request.user.login }}
+          event_body: ${{ github.event.pull_request.body || 'No description provided.' }}
+          event_number: ${{ github.event.pull_request.number }}
+          event_url: ${{ github.event.pull_request.html_url }}

.github/workflows/tf-acc-test.yaml

@@ -27,6 +27,16 @@ jobs:
     name: Acceptance Tests
     runs-on: stackit-docker
     steps:
+      - name: Notify
+        uses: ./.github/actions/notify
+        with:
+          title: Terraform Acceptance Tests started
+          event_title: ${{ github.event.type }}
+          event_author: ${{ github.event.actor.login }}
+          event_body: 'No event body.'
+          event_number: ${{ github.event.id }}
+          event_url: "${{ github.repositoryUrl }}"
+
       - name: Checkout
         uses: actions/checkout@v6
 
@@ -59,3 +69,13 @@ jobs:
           tf_acc_kek_key_ring_id: ${{ vars.TF_ACC_KEK_KEY_RING_ID }}
           tf_acc_kek_key_version: ${{ vars.TF_ACC_KEK_KEY_VERSION }}
           tf_acc_kek_service_account: ${{ vars.TF_ACC_KEK_SERVICE_ACCOUNT }}
+
+      - name: Notify
+        uses: ./.github/actions/notify
+        with:
+          title: Terraform Acceptance Tests finished
+          event_title: ${{ github.event.type }}
+          event_author: ${{ github.event.actor.login }}
+          event_body: 'No event body.'
+          event_number: ${{ github.event.id }}
+          event_url: "${{ github.repositoryUrl }}"