[release-1.6] 🧹 Migrate to buildah action for building multi-arch images

.github/workflows/images/test/eventshub/Containerfile

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+FROM docker.io/library/golang:1.17 AS builder
+
+COPY . /code
+WORKDIR /code
+
+RUN go build \
+  -o ./build/eventshub \
+  ./vendor/knative.dev/reconciler-test/cmd/eventshub
+
+FROM registry.access.redhat.com/ubi8/ubi-minimal:latest
+
+COPY --from=builder /code/build/eventshub /app/eventshub
+
+USER 65532
+
+ENTRYPOINT ["/app/eventshub"]

.github/workflows/images/test/wathola-forwarder/Containerfile

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+FROM docker.io/library/golang:1.17 AS builder
+
+COPY . /code
+WORKDIR /code
+
+RUN go build \
+  -o ./build/wathola-forwarder \
+  ./vendor/knative.dev/eventing/test/test_images/wathola-forwarder
+
+FROM registry.access.redhat.com/ubi8/ubi-minimal:latest
+
+COPY --from=builder /code/build/wathola-forwarder /app/wathola-forwarder
+
+USER 65532
+
+ENTRYPOINT ["/app/wathola-forwarder"]

.github/workflows/multiarch-build.yaml

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+name: Multiarch builds
+
+on:
+  push:
+    branches-ignore:    
+      - 'main'
+      - 'ci/*'
+
+jobs:
+  build-image:
+    name: Build image
+    uses: openshift-knative/hack/.github/workflows/multiarch-containerfile-build.yaml@main
+    secrets: inherit
+    strategy:
+      matrix:
+        image:
+        - eventshub
+        - wathola-forwarder
+    with:
+      image: ${{ matrix.image }}
+      containerfile: .github/workflows/images/test/${{ matrix.image }}/Containerfile