added Arena appliances for fights on a separate server

arena/build.gradle

@@ -0,0 +1,17 @@
+dependencies {
+    implementation project(':common')
+    implementation project(':core')
+
+    compileOnly 'io.papermc.paper:paper-api:26.2.build.129-stable'
+    compileOnly 'org.geysermc.floodgate:api:2.2.4-SNAPSHOT'
+    implementation 'org.apache.httpcomponents:httpclient:4.5.14'
+    implementation 'com.sparkjava:spark-core:2.9.4'
+
+    testImplementation platform('org.junit:junit-bom:5.13.4')
+    testImplementation 'org.junit.jupiter:junit-jupiter'
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+}
+
+test {
+    useJUnitPlatform()
+}