Add ESLint action for Main UI

Signed-off-by: Yannick Schaus <github@schaus.net>

.github/workflows/mainui-eslint.yml

@@ -0,0 +1,48 @@
+# This is a basic workflow to help you get started with Actions
+
+name: Main UI ESLint
+
+on:
+  # Triggers the workflow on push or pull request events but only for the main branch
+  push:
+    branches: [ main ]
+    paths: bundles/org.openhab.ui/web
+  pull_request:
+    branches: [ main ]
+    paths: bundles/org.openhab.ui/web
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+defaults:
+  run:
+    working-directory: bundles/org.openhab.ui/web
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: '12.x'
+
+      - name: Cache node modules
+        id: cache
+        uses: actions/cache@v1
+        with:
+          path: node_modules # npm cache files are stored in `~/.npm` on Linux/macOS
+          key: ${{ runner.os }}-node_modules-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+
+      - name: Install Dependencies
+        run: npm install
+        
+      - name: Run ESLint
+        run: npx eslint src/**/*.js src/**/*.vue