Provide a backwards-compatible sym link in the nimbus-eth2 docker file image

This is needed because commit 0be57ee
changed the location of the nimbus_beacon_node executable within the
container file system. For users, not relying on the official entrypoint
this was a breaking change.

Author: zah

docker/dist/binaries/Dockerfile.bn.amd64

@@ -11,5 +11,10 @@ USER user
 STOPSIGNAL SIGINT
 
 COPY "nimbus-eth2/build/nimbus_beacon_node" "/home/user/nimbus_beacon_node"
+
+RUN mkdir -p /home/user/nimbus-eth2/build && \
+    ln -s /home/user/nimbus_beacon_node /home/user/nimbus-eth2/build/nimbus_beacon_node && \
+    chown -R user:user /home/user/nimbus-eth2/build
+
 WORKDIR "/home/user/"
 ENTRYPOINT ["/home/user/nimbus_beacon_node"]

docker/dist/binaries/Dockerfile.bn.arm

@@ -15,5 +15,10 @@ USER user
 STOPSIGNAL SIGINT
 
 COPY "nimbus-eth2/build/nimbus_beacon_node" "/home/user/nimbus_beacon_node"
+
+RUN mkdir -p /home/user/nimbus-eth2/build && \
+    ln -s /home/user/nimbus_beacon_node /home/user/nimbus-eth2/build/nimbus_beacon_node && \
+    chown -R user:user /home/user/nimbus-eth2/build
+
 WORKDIR "/home/user/"
 ENTRYPOINT ["/home/user/nimbus_beacon_node"]

docker/dist/binaries/Dockerfile.bn.arm64

@@ -15,5 +15,10 @@ USER user
 STOPSIGNAL SIGINT
 
 COPY "nimbus-eth2/build/nimbus_beacon_node" "/home/user/nimbus_beacon_node"
+
+RUN mkdir -p /home/user/nimbus-eth2/build && \
+    ln -s /home/user/nimbus_beacon_node /home/user/nimbus-eth2/build/nimbus_beacon_node && \
+    chown -R user:user /home/user/nimbus-eth2/build
+
 WORKDIR "/home/user/"
 ENTRYPOINT ["/home/user/nimbus_beacon_node"]