feat(plugins): add Velocity proxy and Fabric/Forge/NeoForge/Paper integration mods

Server-side integration plugins: the Velocity proxy plugin plus Fabric, Forge, NeoForge, and Paper mods with a shared module. Gradle build output is not tracked.

plugins/forge/settings.gradle

@@ -0,0 +1,11 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        maven {
+            name = 'MinecraftForge'
+            url = 'https://maven.minecraftforge.net/'
+        }
+    }
+}
+
+rootProject.name = 'felis-forge'