Add PR workflow to run unit tests via github actions.

.github/workflows/pr.yml

@@ -0,0 +1,17 @@
+name: PR
+
+on:
+  pull_request:
+    branches: [ main ]
+
+jobs:
+
+  unit_tests:
+    name: unit tests
+    runs-on: ubuntu-latest
+    container: us.gcr.io/cf-rabbitmq-for-k8s-bunny/rabbitmq-for-kubernetes-ci
+    steps:
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v2
+    - name: Unit tests
+      run: make unit-tests