Automatically install a server on headless environments (#38)

This PR makes the installer automatically install a server on headless environments without needing the `--install-server` option specified. This should reduce user confusion when they try to simply run the jar on a server

build.gradle

@@ -84,7 +84,7 @@ dependencies {
 	testImplementation(platform('org.junit:junit-bom:5.7.2'))
 	testImplementation('org.junit.jupiter:junit-jupiter')
     compileOnly 'org.jetbrains:annotations:24.1.0'
-    testInstallerData 'net.neoforged:neoforge:20.4.76-beta:installer'
+    testInstallerData 'net.neoforged:neoforge:21.4.10-beta:installer'
 }
 
 test {

src/main/java/net/minecraftforge/installer/SimpleInstaller.java

@@ -15,6 +15,7 @@
  */
 package net.minecraftforge.installer;
 
+import java.awt.GraphicsEnvironment;
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileNotFoundException;
@@ -155,6 +156,13 @@ public static void main(String[] args) throws IOException, URISyntaxException {
             }
         }
 
+        if (action == null && GraphicsEnvironment.isHeadless()) {
+            monitor.message("No action was specified but headless environment was detected... Installing server");
+            action = Actions.SERVER;
+            target = optionSet.valueOf(serverInstallOption);
+            ServerInstall.serverStarterJar = true;
+        }
+
         if (action != null) {
             try {
                 SimpleInstaller.headless = true;