bash.#Run: new and improved

* Script is written to filesystem, not inlined as argument
* Pass script either as string, or directory+filename

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

pkg/universe.dagger.io/yarn/test/yarn-test.cue

@@ -33,7 +33,7 @@ dagger.#Plan & {
 				dest:     "/build"
 				contents: pkg.output
 			}
-			script: #"""
+			script: contents: #"""
 				test "$(cat /build/test)" = "output"
 				"""#
 		}