Use pre-built image for action

This will use a prebuilt image that's automatically built for this
repository for each tag by GCB.  This should speed up action execution a
bit.

The version in this repo will still run from the local code though, so
we can still fix bugs.  That configuration lives in the `action-nightly`
subdirectory, and can also be referenced by external projects.

.github/workflows/main.yml

@@ -11,6 +11,6 @@ jobs:
       uses: actions/checkout@v2
     - name: Verifier action
       id: verifier
-      uses: ./
+      uses: ./action-nightly
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}

action-nightly/action.yml

@@ -0,0 +1,9 @@
+name: 'Verify KubeBuilder PRs'
+description: 'Verify PRs for the KubeBuilder project repos & similar'
+inputs:
+  github_token:
+    description: "the github_token provided by the actions runner"
+    required: true
+runs:
+  using: docker
+  image: '../Dockerfile'

action.yml

@@ -6,4 +6,7 @@ inputs:
     required: true
 runs:
   using: docker
-  image: 'Dockerfile'
+  # this is built using GCB by building the Dockerfile in this directory on
+  # every tagged release.  After tagging a release, a new version should
+  # automatically appear.
+  image: 'docker://gcr.io/kubebuilder/pr-verifier:v0.1.1'