Local testing via Makefile & Docker (#19981)

docker-compose.yml

@@ -0,0 +1,19 @@
+version: "3.8"
+services:
+  # The main image: this doesn't run any particular command, but is mainly used
+  # for running tests locally
+  marlin:
+    image: marlin-dev
+    build:
+      dockerfile: Dockerfile
+      context: docker
+    working_dir: /code
+    volumes:
+    - .:/code
+    - platformio-cache:/root/.platformio
+
+volumes:
+  # This volume holds installed libraries for PlatformIO. If this is deleted you
+  # will have to download all the dependencies again, which can be a very slow
+  # process
+  platformio-cache: