[WIP] Add GitHub action: Greetings.yml - Automates advice to JabRefs …

…first time code contributors (#9272)

* Greetings.yml

Introduction for first time contributors to JabRef.
Triggers upon assignment and also upon first pull-request

* Add greetings message and removes trigger for PRs

.github/workflows/greetings.yml

@@ -0,0 +1,19 @@
+name: Greetings
+
+on: 
+  issues:
+     types: assigned
+
+jobs:
+  greeting:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+    - uses: actions/first-interaction@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        issue-message: "As a general advice for newcomers: check out https://github.com/JabRef/jabref/blob/main/CONTRIBUTING.md for a start. Also, https://devdocs.jabref.org/getting-into-the-code/guidelines-for-setting-up-a-local-workspace is worth having a look at. Feel free to ask if you have any questions here on GitHub or also at JabRef's [Gitter](https://gitter.im/JabRef/jabref) chat.
+
+Try to open a (draft) pull request early on, so that people can see you are working on the issue and so that they can see the direction the pull request is heading towards. This way, you will likely receive valuable feedback."