Add CI workflow to do Arduino project-specific linting

On every push, pull request, and periodically, run Arduino Lint to check for common problems not related to the project
code.

Author: per1234

.github/workflows/check-arduino.yml

@@ -0,0 +1,27 @@
+name: Check Arduino
+
+# See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
+on:
+  push:
+  pull_request:
+  schedule:
+    # Run every Tuesday at 8 AM UTC to catch breakage caused by new rules added to Arduino Lint.
+    - cron: "0 8 * * TUE"
+  workflow_dispatch:
+  repository_dispatch:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Arduino Lint
+        uses: arduino/arduino-lint-action@v1
+        with:
+          compliance: specification
+          library-manager: update
+          # Always use this setting for official repositories. Remove for 3rd party projects.
+          official: true

README.md

@@ -1,5 +1,7 @@
 `ArduinoIoTCloud`
 =================
+
+[![Check Arduino status](https://github.com/arduino-libraries/ArduinoIoTCloud/actions/workflows/check-arduino.yml/badge.svg)](https://github.com/arduino-libraries/ArduinoIoTCloud/actions/workflows/check-arduino.yml)
 [![Compile Examples](https://github.com/arduino-libraries/ArduinoIoTCloud/workflows/Compile%20Examples/badge.svg)](https://github.com/arduino-libraries/ArduinoIoTCloud/actions?workflow=Compile+Examples)
 [![Spell Check](https://github.com/arduino-libraries/ArduinoIoTCloud/workflows/Spell%20Check/badge.svg)](https://github.com/arduino-libraries/ArduinoIoTCloud/actions?workflow=Spell+Check)
 [![Unit Tests](https://github.com/arduino-libraries/ArduinoIoTCloud/workflows/Unit%20Tests/badge.svg)](https://github.com/arduino-libraries/ArduinoIoTCloud/actions?workflow=Unit+Tests)