Add Github Action check to make sure template UI is unchanged (#918)

.github/workflows/main.yml

@@ -299,6 +299,8 @@ jobs:
           python-version: 3.8
       - name: Install wpiformat
         run: pip3 install wpiformat
+      - name: Check index.html not changed
+        run: git --no-pager diff --exit-code origin/master photon-server/src/main/resources/web/index.html
       - name: Run
         run: wpiformat
       - name: Check output

.gitignore

@@ -159,3 +159,4 @@ photonlib-cpp-examples/*/vendordeps/*
 
 */networktables.json
 *.sqlite
+photon-server/src/main/resources/web/index.html