fix: add missing backslash for volume extraArgs in helm chart (#7676)

Fixes #7467

The -mserver argument line in volume-statefulset.yaml was missing a
trailing backslash, which prevented extraArgs from being passed to
the weed volume process.

Also:
- Extracted master server list generation logic into shared helper
  templates in _helpers.tpl for better maintainability
- Updated all occurrences of deprecated -mserver flag to -master
  across docker-compose files, test files, and documentation

test/s3/iam/Makefile

@@ -75,7 +75,7 @@ start-services: ## Start SeaweedFS services for testing
 		-dataCenter=dc1 -rack=rack1 \
 		-dir=test-volume-data \
 		-max=100 \
-		-mserver=localhost:$(MASTER_PORT) > weed-volume.log 2>&1 & \
+		-master=localhost:$(MASTER_PORT) > weed-volume.log 2>&1 & \
 		echo $$! > $(VOLUME_PID_FILE)
 	
 	@echo "Waiting for volume server to be ready..."

test/s3/iam/docker-compose.test.yml

@@ -21,7 +21,7 @@ services:
   seaweedfs-volume:
     image: chrislusf/seaweedfs:latest
     container_name: seaweedfs-volume-test
-    command: volume -dir=/data -port=8083 -mserver=seaweedfs-master:9333
+    command: volume -dir=/data -port=8083 -master=seaweedfs-master:9333
     ports:
       - "8083:8083"
     volumes:

test/s3/iam/docker-compose.yml

@@ -51,7 +51,7 @@ services:
     ports:
       - "8083:8083"
       - "18083:18083"
-    command: "volume -ip=weed-volume -port=8083 -dir=/data -mserver=weed-master:9333 -dataCenter=dc1 -rack=rack1"
+    command: "volume -ip=weed-volume -port=8083 -dir=/data -master=weed-master:9333 -dataCenter=dc1 -rack=rack1"
     volumes:
       - volume-data:/data
     networks: