Restructure Build & Deploy sequence in CI

I've restructured the build & deploy sequence in our GitHub Actions CI
workflow:

- There's now a separate workflow to deploy to our cluster

- The Build workflow has an additional `if` check to ensure we're only
  starting the build & deploy sequences for pushes to master

- We now checkout the python-discord/kubernetes repo to fetch the
  deployment.yaml file located in there

.github/workflows/build-deploy.yaml → .github/workflows/build.yaml

@@ -1,4 +1,4 @@
-name: Build & Deploy
+name: Build
 
 on:
   workflow_run:
@@ -9,9 +9,9 @@ on:
       - completed
 
 jobs:
-  build-and-deploy:
-    name: Build and Deploy to Kubernetes
-    if: github.event.workflow_run.conclusion == 'success'
+  build:
+    name: Build Docker Image
+    if: github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.event == 'push'
     runs-on: ubuntu-latest
 
     steps:
@@ -54,17 +54,3 @@ jobs:
           tags: |
             ghcr.io/python-discord/site:latest
             ghcr.io/python-discord/site:${{ steps.sha_tag.outputs.tag }}
-
-      - name: Authenticate with Kubernetes
-        uses: azure/k8s-set-context@v1
-        with:
-          method: kubeconfig
-          kubeconfig: ${{ secrets.KUBECONFIG }}
-
-      - name: Deploy to Kubernetes
-        uses: Azure/k8s-deploy@v1
-        with:
-          manifests: |
-              deployment.yaml
-          images: 'ghcr.io/python-discord/site:${{ steps.sha_tag.outputs.tag }}'
-          kubectl-version: 'latest'

.github/workflows/kubernetes-deployment.yaml

@@ -0,0 +1,45 @@
+name: Deploy
+
+on:
+  workflow_run:
+    workflows: ["Build"]
+    branches:
+      - master
+    types:
+      - completed
+
+jobs:
+  deploy:
+    if: github.event.workflow_run.conclusion == 'success'
+    name: Deploy to Kubernetes Cluster
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Create SHA Container Tag
+        id: sha_tag
+        run: |
+          tag=$(cut -c 1-7 <<< $GITHUB_SHA)
+          echo "::set-output name=tag::$tag"
+
+      # Check out the private Kubernetes repository for the
+      # deployment.yaml file using a GitHub Personal Access
+      # Token to get access.
+      - name: Checkout code
+        uses: actions/checkout@v2
+        with:
+          repository: python-discord/kubernetes
+          token: ${{ secrets.REPO_TOKEN }}
+
+      - name: Authenticate with Kubernetes
+        uses: azure/k8s-set-context@v1
+        with:
+          method: kubeconfig
+          kubeconfig: ${{ secrets.KUBECONFIG }}
+
+      - name: Deploy to Kubernetes
+        uses: Azure/k8s-deploy@v1
+        with:
+          manifests: |
+              site/deployment.yaml
+          images: 'ghcr.io/python-discord/site:${{ steps.sha_tag.outputs.tag }}'
+          kubectl-version: 'latest'