make+release.sh: add release helper script for docker

Makefile

@@ -81,6 +81,10 @@ release:
 	rm -rf chantools-v*
 	./release.sh build-release "$(VERSION_TAG)" "$(BUILD_SYSTEM)" "$(RELEASE_LDFLAGS)"
 
+docker-release:
+	@$(call print, "Creating docker release of chantools.")
+	./release.sh docker-release "$(VERSION_TAG)"
+
 docker-tools:
 	@$(call print, "Building tools docker image.")
 	docker build -q -t chantools-tools $(TOOLS_DIR)

release.sh

@@ -10,6 +10,7 @@
 set -e
 
 PKG="github.com/lightninglabs/chantools"
+DOCKER_USER="guggero"
 PACKAGE=chantools
 
 # green prints one line of green text (if the terminal supports it).
@@ -79,6 +80,13 @@ function build_release() {
   shasum -a 256 * >manifest-$tag.txt
 }
 
+# docker_release builds the Docker images for all supported platforms.
+#   arguments: <version-tag>
+function docker_release() {
+  local tag=$1
+  docker buildx build --platform linux/arm64,linux/amd64 --tag $DOCKER_USER/$PACKAGE:$tag --output "type=registry" .
+}
+
 # usage prints the usage of the whole script.
 function usage() {
   red "Usage: "
@@ -103,6 +111,10 @@ build-release)
   green "Building release"
   build_release "$@"
   ;;
+docker-release)
+  green "Building docker release"
+  docker_release "$@"
+  ;;
 *)
   usage
   exit 1