Add workflow to build and test docker image

.github/workflows/docker_stable.yaml

@@ -1,4 +1,5 @@
-# Build and push latest docker image on push to master branch
+# Build and push docker image on push to 'stable' branch
+# Docker build will be uploaded to dockerhub with the 'inventree:stable' tag
 
 name: Docker Build
 

.github/workflows/docker_tag.yaml

@@ -1,4 +1,5 @@
-# Publish docker images to dockerhub
+# Publish docker images to dockerhub on a tagged release
+# Docker build will be uploaded to dockerhub with the 'invetree:<tag>' tag
 
 name: Docker Publish
 

.github/workflows/docker_test.yaml

@@ -0,0 +1,41 @@
+# Test that the InvenTree docker image compiles correctly
+
+# This CI action runs on pushes to either the master or stable branches
+
+# 1. Build the development docker image (as per the documentation)
+# 2. Install requied python libs into the docker container
+# 3. Launch the container
+# 4. Check that the API endpoint is available
+
+name: Docker Test
+
+on:
+  push:
+    branches:
+      - 'master'
+      - 'stable'
+
+  pull_request:
+    branches-ignore:
+      - l10*
+
+jobs:
+
+  docker:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@v2
+      - name: Build Docker Image
+        run: |
+          cd docker
+          docker-compose -f docker-compose.dev.yml build
+          docker-compose -f docker-compose.dev.yml run inventree-dev-server invoke update
+          docker-compose -f docker-compose.dev.yml up -d
+      - name: Sleepy Time
+        run: sleep 60
+      - name: Test API
+        run: |
+          pip install requests
+          python3 ci/check_api_endpoint.py