Implement build precheck (#85)

This PR introduces a build step pre-check on GitHub actions that will be
triggered every time a new PR against develop is created.

How it
works:


1. Dev opens PR to develop
2. Skaffold build is triggered
3. If new modifications are done to the PR while its open step 2 is
re-triggered
4. After PR is merged the normal pipeline gets executed
(build+push+deploy)
5. You can't get your PR merged if the pre-check pipeline isn't green,
so it needs to finish first

To achieve this:
- New pipeline kread-skaffold-precheck.yml
- Branch protection rule at repo level

---------

Co-authored-by: Synthetics <[email protected]>

.github/workflows/kread-skaffold-precheck.yml

@@ -0,0 +1,33 @@
+name: Skaffold Build PR Check
+
+on:
+  pull_request:
+    branches:
+      - develop
+    types:
+      - opened
+      - synchronize
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout Repository
+      uses: actions/checkout@v2
+
+    - name: Install Skaffold 
+      run: |
+        curl -Lo skaffold https://storage.googleapis.com/skaffold/releases/latest/skaffold-linux-amd64
+        sudo install skaffold /usr/local/bin/
+      shell: bash
+
+    - name: Skaffold build precheck
+      run: |
+        cd frontend
+        export $(grep -v '^#' .env.emerynet | xargs)
+        envsubst < skaffold.precheck.yaml > skaffold.emerynet.yaml
+        skaffold build --filename skaffold.emerynet.yaml
+      shell: bash
+
+

frontend/skaffold.precheck.yaml

@@ -0,0 +1,19 @@
+apiVersion: skaffold/v2beta27
+kind: Config
+metadata:
+  name: character-builder-ui
+build:
+  tagPolicy:
+    sha256: {}
+  local:
+    concurrency: 0
+    push: false
+  artifacts:
+    - image: precheck
+      docker:
+        dockerfile: Dockerfile.ui
+        buildArgs:
+          VITE_RPC: "emerynet.rpc.agoric.net"
+          VITE_BRIDGE_HREF: "" 
+          VITE_BASE_URL: "kryha.kread.dev"
+          VITE_NETWORK_CONFIG: "https://emerynet.agoric.net/network-config"