ci: Initial self-hosted end-to-end unified CI setup (#1592)

This is work as part of
getsentry/self-hosted#1756

Essentially, we want to move from Google Cloudbuild to a centralized
Github Action that can be used across Sentry/Snuba/Relay/self-hosted.
This adds a job which should use that action.

#skip-changelog

.github/workflows/ci.yml

@@ -359,3 +359,42 @@ jobs:
         run: |
           echo "Testing against ${RELAY_TEST_IMAGE}"
           make test-relay-integration
+
+
+  self-hosted-end-to-end:
+    needs: []
+    runs-on: ubuntu-latest
+    # temporary, remove once we are confident the action is working
+    continue-on-error: true
+
+    steps:
+      # TODO: move image build to its own step once we can push them
+      - name: Checkout Relay
+        uses: actions/checkout@v3
+        with:
+          submodules: recursive
+      - name: Try pulling Relay images
+        shell: bash
+        # We don't need these but they might make things faster
+        continue-on-error: true
+        run: |
+          docker pull us.gcr.io/getsentry/relay:nightly
+          docker pull us.gcr.io/getsentry/relay:deps
+      - name: Build Relay first stage
+        run: |
+          docker build --target relay-deps -t ghcr.io/getsentry/relay:deps \
+            --cache-from us.gcr.io/getsentry/relay:deps \
+            .
+      - name: Build Relay final image
+        run: |
+          docker build -t ghcr.io/getsentry/relay:nightly -t ghcr.io/getsentry/relay:${{ github.sha }} \
+            --cache-from us.gcr.io/$PROJECT_ID/relay:deps \
+            --cache-from us.gcr.io/$PROJECT_ID/relay:nightly \
+            .
+      # TODO: push the image here
+      - name: Run Sentry self-hosted e2e CI
+        uses: getsentry/action-self-hosted-e2e-tests@5bbd3d6725bbe4bf5cc12f8a3291ce87df6a891f
+        with:
+          project_name: relay
+          local_image: ghcr.io/getsentry/relay:${{ github.sha }}
+          docker_repo: ghcr.io/getsentry/relay