Simplify docker.#Run

* `cmd` is renamed to `command` for readability
  * `script` is removed. Feature moves up the stack (bash.#Run,
    python.#Run)

Signed-off-by: Solomon Hykes <solomon@dagger.io>

pkg/universe.dagger.io/docker/test/run-command-test.cue

@@ -13,7 +13,7 @@ dagger.#Plan & {
 
 		run: docker.#Run & {
 			"image": image.output
-			cmd: {
+			command: {
 				name: "/bin/sh"
 				args: ["-c", "echo -n hello world >> /output.txt"]
 			}