Support multiple values for COPY_PLUGINS_SRC, COPY_MODS_SRC, and COPY_CONFIG_SRC (#3377)

examples/paper/compose.yml

@@ -0,0 +1,16 @@
+services:
+  mc:
+    image: itzg/minecraft-server
+    tty: true
+    stdin_open: true
+    environment:
+      EULA: "true"
+      TYPE: PAPER
+      MEMORY: 2G
+    ports:
+      - "25565:25565"
+    volumes:
+      - mc-data:/data
+    restart: unless-stopped
+volumes:
+  mc-data: {}