github: Build and push container image for pull requests

This change adds container builds for pull requests. For two reasons:

1) In case of failures on the main branch, to check whether a pull
   request aiming to fix them really fixes them.
2) Might be nice for testing someones' changes before merging, without
   necessity to check out and build their code.

Signed-off-by: Michal Rostecki <[email protected]>

Author: vadorovsky

.github/workflows/container-image.yml

@@ -4,6 +4,9 @@ on:
     - main
     tags:
     - 'v*'
+  pull_request:
+    branches:
+    - main
 
 name: build container image
 
@@ -39,6 +42,25 @@ jobs:
           push: true
           tags: |
             ghcr.io/rancher-sandbox/lockc:latest
+      -
+        name: Retrieve pull request number
+        if: ${{ startsWith(github.ref, 'refs/pull/') }}
+        run: |
+          echo PR_NUMBER=$(echo $GITHUB_REF | sed -e "s|^refs/pull/||" -e "s|/merge$||")
+      -
+        name: Build and push pull request container image
+        if: ${{ startsWith(github.ref, 'refs/pull/') }}
+        users: docker/build-push-action@v2
+        with:
+          context: .
+          file: ./Dockerfile
+          platforms: linux/amd64, linux/arm64
+          push: true
+          tags: |
+            ghcr.io/rancher-sandbox/lockc:pr${{ env.PR_NUMBER }}
+      - name: Get ref
+        run: |
+          echo $GITHUB_REF
       -
         name: Retrieve tag name
         if: ${{ startsWith(github.ref, 'refs/tags/') }}