dockerfile,e2e: Use buildx and cache mounts for faster rebuilds in E2E

Dockerfile

@@ -8,22 +8,26 @@ WORKDIR /workspace
 ENV GO111MODULE=on \
   CGO_ENABLED=0
 
-# Copy the Go Modules manifests
-COPY go.mod go.sum ./
+# # Copy the Go Modules manifests
+# COPY go.mod go.sum ./
 
-# cache deps before building and copying source so that we don't need to re-download as much
-# and so that source changes don't invalidate our downloaded layer
-RUN go mod download
+# # cache deps before building and copying source so that we don't need to re-download as much
+# # and so that source changes don't invalidate our downloaded layer
+# RUN --mount=type=cache,target=/go/pkg/mod go mod download
 
 # Copy the go source
-COPY . .
+# COPY . .
+
+ARG TARGETOS
+ARG TARGETARCH
 
 # Build
-RUN export GOOS=$(echo ${TARGETPLATFORM} | cut -d / -f1) && \
-  export GOARCH=$(echo ${TARGETPLATFORM} | cut -d / -f2) && \
-  GOARM=$(echo ${TARGETPLATFORM} | cut -d / -f3 | cut -c2-) && \
-  go build -a -o manager main.go && \
-  go build -a -o github-webhook-server ./cmd/githubwebhookserver
+RUN --mount=target=. \
+  --mount=type=cache,mode=0777,target=/root/.cache/go-build \
+  --mount=type=cache,mode=0777,target=/go/pkg/mod\
+  GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
+  GOARM=$(echo ${TARGETPLATFORM} | cut -d / -f3 | cut -c2-) \
+  go build -o /out/manager main.go && go build -o /out/github-webhook-server ./cmd/githubwebhookserver
 
 # Use distroless as minimal base image to package the manager binary
 # Refer to https://github.com/GoogleContainerTools/distroless for more details
@@ -31,8 +35,8 @@ FROM gcr.io/distroless/static:nonroot
 
 WORKDIR /
 
-COPY --from=builder /workspace/manager .
-COPY --from=builder /workspace/github-webhook-server .
+COPY --from=builder /out/manager .
+COPY --from=builder /out/github-webhook-server .
 
 USER nonroot:nonroot