Add template for unity upgrade workflow

Author: JohannesDeml

.github/templates/upgrade-unity-pr-body.md

@@ -0,0 +1,14 @@
+## [Automated Workflow] Upgrade unity to {{ .unityversion }}
+
+>  [workflow file](https://github.com/JohannesDeml/UnityWebGL-LoadingTest/blob/master/.github/workflows/upgrade-unity.yml) using [create-pull-request](https://github.com/peter-evans/create-pull-request) & [render-template](https://github.com/chuhlomin/render-template)
+
+### Built version demos
+
+* https://deml.io/experiments/unity-webgl/{{ .unityversion }}-webgl2
+* https://deml.io/experiments/unity-webgl/{{ .unityversion }}-webgl1
+
+### Other links
+
+* [All builds](https://deml.io/experiments/unity-webgl)
+* [Game CI docker images](https://game.ci/docs/docker/versions)
+* [Unity Download Archive](https://unity.com/releases/editor/archive) 

.github/workflows/upgrade-unity.yml

@@ -1,4 +1,5 @@
 # Manually upgrade unity and update packages
+# Check if the Unity version already exists as a docker image: https://game.ci/docs/docker/versions
 name: Upgrade Unity version
 
 on:
@@ -117,14 +118,23 @@ jobs:
           GIT_USER: ${{ github.actor }}
 
 
+      - name: Render template
+        id: template
+        uses: chuhlomin/render-template@v1.4
+        with:
+          template: .github/templates/upgrade-unity-pr-body.md
+          vars: |
+            unityversion: ${{ steps.upgrade_name.outputs.NAME }}
+
       - name: Create Pull Request
         uses: peter-evans/create-pull-request@v4
         with:
           token: ${{ secrets.PR_GITHUB_TOKEN }}
           commit-message: "[Automated workflow] upgrade-unity from ${{steps.last_unity_version.outputs.VERSION}} to ${{ inputs.unityVersion }}"
           branch: "ci/upgrade-unity/from-${{steps.last_unity_version.outputs.VERSION}}-to-${{ steps.upgrade_name.outputs.NAME }}"
           delete-branch: true
-          title: "[Automated workflow] upgrade-unity from ${{steps.last_unity_version.outputs.VERSION}} to ${{ inputs.unityVersion }} - URP: ${{ inputs.urp }}"
+          title: "[Automated workflow] upgrade-unity from ${{steps.last_unity_version.outputs.VERSION}} to ${{ steps.upgrade_name.outputs.NAME }}"
+          body: ${{ steps.template.outputs.result }}
 
       - name: Add tags
         run: |