bake: initial implementation

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

hack/demo-env/examples/compose/config.hcl

@@ -0,0 +1,34 @@
+group "default" {
+	targets = ["db", "webapp"]
+}
+
+group "release" {
+	targets = ["db", "webapp-plus"]
+}
+
+target "db" {
+	context = "./"
+	tags = ["docker.io/tonistiigi/db"]
+}
+
+target "webapp" {
+	context = "./"
+	dockerfile = "Dockerfile.webapp"
+	args = {
+		buildno = "123"
+	}
+}
+
+target "cross" {
+	platforms = [
+		"linux/amd64",
+		"linux/arm64"
+	]
+}
+
+target "webapp-plus" {
+	inherits = ["webapp", "cross"]
+	args = {
+		IAMPLUS = "true"
+	}
+}