rename engine.#Build to engine.#Dockerfile

Signed-off-by: Richard Jones <richard@dagger.io>

tests/tasks/dockerfile/image_config.cue

@@ -0,0 +1,26 @@
+package testing
+
+import (
+	"dagger.io/dagger/engine"
+)
+
+engine.#Plan & {
+	inputs: directories: testdata: path: "./testdata"
+
+	actions: {
+		// FIXME: this doesn't test anything beside not crashing
+		build: engine.#Dockerfile & {
+			source: inputs.directories.testdata.contents
+			dockerfile: contents: """
+				FROM alpine:latest@sha256:ab00606a42621fb68f2ed6ad3c88be54397f981a7b70a79db3d1172b11c4367d
+				ENV test foobar
+				CMD /test-cmd
+				"""
+		} & {
+			config: {
+				Env: ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin", "test=foobar"]
+				Cmd: ["/bin/sh", "-c", "/test-cmd"]
+			}
+		}
+	}
+}