Add bake-file output (#36)

Co-authored-by: CrazyMax <crazy-max@users.noreply.github.com>

test/docker-bake.hcl

@@ -0,0 +1,38 @@
+target "ghaction-docker-meta" {}
+
+group "default" {
+  targets = ["db", "app"]
+}
+
+group "release" {
+  targets = ["db", "app-plus"]
+}
+
+target "db" {
+  context = "./test"
+  tags = ["docker.io/tonistiigi/db"]
+}
+
+target "app" {
+  inherits = ["ghaction-docker-meta"]
+  context = "./test"
+  dockerfile = "Dockerfile"
+  args = {
+    name = "foo"
+  }
+}
+
+target "cross" {
+  platforms = [
+    "linux/amd64",
+    "linux/arm64",
+    "linux/386"
+  ]
+}
+
+target "app-plus" {
+  inherits = ["app", "cross"]
+  args = {
+    IAMPLUS = "true"
+  }
+}