Migrate everything on Gradle

Also added tasks to run the server & client separately

ChatApp/app/build.gradle

@@ -0,0 +1,65 @@
+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Java application project to get you started.
+ * For more details on building Java & JVM projects, please refer to https://docs.gradle.org/8.13/userguide/building_java_projects.html in the Gradle documentation.
+ */
+
+plugins {
+    // Apply the application plugin to add support for building a CLI application in Java.
+    id 'application'
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+    // Use JUnit Jupiter for testing.
+    testImplementation libs.junit.jupiter
+
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+
+    // This dependency is used by the application.
+    implementation libs.guava
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+application {
+    // Define the main class for the application.
+    mainClass = 'ChatApp'
+}
+
+run {
+    standardInput = System.in
+}
+
+
+
+tasks.named('test') {
+    // Use JUnit Platform for unit tests.
+    useJUnitPlatform()
+}
+
+tasks.register("server", JavaExec){
+    group = "ChatAppConsole"
+    description = "Runs the server + the admin client"
+    mainClass.set("ChatApp")
+    classpath = sourceSets.main.runtimeClasspath
+    standardInput = System.in
+}
+
+tasks.register("client", JavaExec) {
+    group = "ChatAppConsole"
+    description = "Runs the client"
+    mainClass.set("ChatAppClient")
+    classpath = sourceSets.main.runtimeClasspath
+    standardInput = System.in
+}