Add scripts/build-release-linux.sh for building musl-linked release
archives (x86_64 and aarch64) on Linux. Uses `cross` for cross-
compilation so no host toolchain beyond Docker/Podman is required.
Also add mdrs-*.tar.gz and mdrs-*.zip to .gitignore to prevent
generated release archives from being tracked.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
