Make Dockerfile more reliable for multiarch

Dockerfile

@@ -1,20 +1,19 @@
 # We can't use alpine anymore because crypto has rust deps.
-FROM node:18-slim
+FROM --platform=$BUILDPLATFORM node:18-slim AS build
 # install git
 RUN apt-get update && \
     apt-get install -y git\
     &&  rm -rf /var/lib/apt/lists/*
-COPY . /tmp/src
-RUN cd /tmp/src \
-    && yarn install --network-timeout 100000 \
-    && yarn build \
-    && mv lib/ /mjolnir/ \
-    && mv node_modules / \
-    && mv mjolnir-entrypoint.sh / \
-    && mv package.json / \
-    && mv version.txt / \
-    && cd / \
-    && rm -rf /tmp/*
+COPY . .
+RUN yarn install --network-timeout 100000 \
+    && yarn build
+
+FROM node:18-slim
+
+COPY --from=build /lib /mjolnir
+COPY --from=build /node_modules /node_modules
+COPY --from=build mjolnir-entrypoint.sh .
+COPY --from=build version.txt .
 
 ENV NODE_ENV=production
 ENV NODE_CONFIG_DIR=/data/config