Add x64 linux packaging, improve default run.sh gen for load balancing servers

build_x86_64.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+# requires cargo cross (cargo install cross)
+cross build --release --all --target x86_64-unknown-linux-musl
+
+./utils/package_release.py ./target/x86_64-unknown-linux-musl/release/ --output openjam_servers_linux_x86_64.zip