Add Docker multiarch support

contrib/docker/Dockerfile.multiarch

@@ -0,0 +1,29 @@
+# syntax=docker/dockerfile:1
+FROM --platform=$BUILDPLATFORM docker.io/golang:alpine as builder
+
+COPY . /src
+WORKDIR /src
+
+ARG TARGETOS
+ARG TARGETARCH
+ENV CGO_ENABLED=0
+ENV GOOS=${TARGETOS} GOARCH=${TARGETARCH}
+
+RUN GOOS=${TARGETOS} GOARCH=${TARGETARCH} apk add git && ./build && go build -o /src/genkeys cmd/genkeys/main.go
+
+FROM docker.io/alpine
+
+COPY --from=builder /src/yggdrasil /usr/bin/yggdrasil
+COPY --from=builder /src/yggdrasilctl /usr/bin/yggdrasilctl
+COPY --from=builder /src/genkeys /usr/bin/genkeys
+COPY contrib/docker/entrypoint.sh /usr/bin/entrypoint.sh
+
+# RUN addgroup -g 1000 -S yggdrasil-network \
+#  && adduser -u 1000 -S -g 1000 --home /etc/yggdrasil-network yggdrasil-network
+#
+# USER yggdrasil-network
+# TODO: Make running unprivileged work
+
+VOLUME [ "/etc/yggdrasil-network" ]
+
+ENTRYPOINT [ "/usr/bin/entrypoint.sh" ]