feat: use env var to add incubator java option

use the variable test operator to save line length

Author: vordimous

manager/src/main/java/io/aklivity/zilla/manager/internal/commands/install/ZpmInstall.java

@@ -704,6 +704,7 @@ private void generateLauncher() throws IOException
         Path zillaPath = launcherDir.resolve("zilla");
         Files.write(zillaPath, Arrays.asList(
                 "#!/bin/sh",
+                "JAVA_OPTIONS+=\"${ZILLA_INCUBATOR_ENABLED:+ -Dzilla.incubator.enabled=$ZILLA_INCUBATOR_ENABLED}\"",
                 "cd \"${0%/*}\"",
                 String.format(String.join(" ", Arrays.asList(
                     "exec %s/bin/java",