Refactor workflows - user reusable workflows (#2504)

Signed-off-by: Avgustin Marinov <Avgustin.Marinov@bosch.com>

.github/workflows/first-interaction.yaml

@@ -0,0 +1,22 @@
+name: First User Interaction
+
+on:
+  pull_request_target:
+    types: [ opened ]
+
+permissions:
+  contents: read
+
+jobs:
+  greeting:
+    # only on original eclipse-hawkbit/hawkbit repo
+    if: github.repository == 'eclipse-hawkbit/hawkbit'
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/first-interaction@v1
+        with:
+          repo-token: ${{ secrets.PAT_SECRET }}
+          pr-message: |-
+            Thanks @${{ github.actor }} for taking the time to contribute to hawkBit! We really appreciate this. Make yourself comfortable while I'm looking for a committer to help you with your contribution.
+            Please make sure you read the [contribution guide](https://github.com/eclipse-hawkbit/hawkbit/blob/master/CONTRIBUTING.md) and signed the Eclipse Contributor Agreement (ECA).