Add a github action that automatically create tag on master.

This action will add a tag matching ROUTEROS release once master
pass the CI step after a push to master (can be the result of direct
push, PR merge, ...).

This tag being pushed will trigger the CD github action which will
push the docker image that match this tag to docker hub.

.github/workflows/tag.yml

@@ -0,0 +1,36 @@
+name: "Tag master with new version of RouterOS when CI pass"
+
+on:
+  push:
+    branches:
+      - "master"
+
+permissions:
+  contents: write
+  pull-requests: read
+
+jobs:
+  call_test:
+    uses: EvilFreelancer/docker-routeros/.github/workflows/ci.yml@master
+
+  tag:
+    name: "Add a tag to git"
+    runs-on: "ubuntu-latest"
+    needs: call_test
+    if: always() && needs.call_test.result == 'success'
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+            fetch-depth: '0'
+
+      - name: Add new tag on git
+        run: |
+          NEW_TAG=$(grep 'ROUTEROS_VERSION="' Dockerfile |cut -d '"' -f 2)
+          git config user.name 'GitHub Actions'
+          git config user.email 'github-actions@users.noreply.github.com'
+          git tag "$NEW_TAG"
+
+      - name: Push new tag to git
+        if: ${{ !env.ACT }}
+        run: git push origin "$NEW_TAG"