feat: add support for arm64 (#142)

- set explicit action permissions
- make package owner dynamic so forks can test workflow
- build multi platform images using cross compilation amd64 -> arm64
- add a scope to buildx gha cache

scripts/build-image-layer.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+
+set -eu
+
+case "${TARGETARCH}" in
+  "amd64")
+    LINKER_NAME="x86_64-linux-gnu-gcc"
+    LINKER_PACKAGE="gcc-x86-64-linux-gnu"
+    BUILD_TARGET="x86_64-unknown-linux-gnu" ;;
+  "arm64")
+    LINKER_NAME="aarch64-linux-gnu-gcc"
+    LINKER_PACKAGE="gcc-aarch64-linux-gnu"
+    BUILD_TARGET="aarch64-unknown-linux-gnu" ;;
+esac
+
+tools() {
+  apt-get install -y "${LINKER_PACKAGE}"
+  rustup target add "${BUILD_TARGET}"
+}
+
+deps() {
+  mkdir -p \
+    crates/bonfire/src \
+    crates/delta/src \
+    crates/quark/src
+  echo 'fn main() { panic!("stub"); }' |
+    tee crates/bonfire/src/main.rs |
+    tee crates/delta/src/main.rs
+  echo '' |
+    tee crates/quark/src/lib.rs
+  cargo build --locked --release --target "${BUILD_TARGET}"
+}
+
+apps() {
+  touch -am \
+    crates/bonfire/src/main.rs \
+    crates/delta/src/main.rs \
+    crates/quark/src/lib.rs
+  cargo build --locked --release --target "${BUILD_TARGET}"
+  mv target _target && mv _target/"${BUILD_TARGET}" target
+}
+
+export RUSTFLAGS="-C linker=${LINKER_NAME}"
+export PKG_CONFIG_ALLOW_CROSS="1"
+export PKG_CONFIG_PATH="/usr/lib/pkgconfig:/usr/lib/aarch64-linux-gnu/pkgconfig:/usr/lib/x86_64-linux-gnu/pkgconfig"
+
+"$@"