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

seaweedfs-rdma-sidecar/docker-compose.mount-rdma.yml

@@ -32,7 +32,7 @@ services:
       - "18080:18080"
     command: >
       volume
-      -mserver=seaweedfs-master:9333
+      -master=seaweedfs-master:9333
       -port=8080
       -dir=/data
       -max=100

seaweedfs-rdma-sidecar/docker-compose.rdma-sim.yml

@@ -21,7 +21,7 @@ services:
   seaweedfs-volume:
     image: chrislusf/seaweedfs:latest
     container_name: seaweedfs-volume
-    command: volume -mserver=seaweedfs-master:9333 -ip=seaweedfs-volume -port=8080 -dir=/data
+    command: volume -master=seaweedfs-master:9333 -ip=seaweedfs-volume -port=8080 -dir=/data
     ports:
       - "8080:8080"
     volumes:

seaweedfs-rdma-sidecar/docker-compose.yml

@@ -21,7 +21,7 @@ services:
   seaweedfs-volume:
     image: chrislusf/seaweedfs:latest
     container_name: seaweedfs-volume
-    command: volume -mserver=seaweedfs-master:9333 -ip=seaweedfs-volume -port=8080 -dir=/data
+    command: volume -master=seaweedfs-master:9333 -ip=seaweedfs-volume -port=8080 -dir=/data
     ports:
       - "8080:8080"
     volumes:

seaweedfs-rdma-sidecar/scripts/demo-mount-rdma.sh

@@ -107,7 +107,7 @@ wait_for_service "Master" "http://localhost:9333/cluster/status"
 
 # Start SeaweedFS Volume Server
 echo -e "${BLUE}💾 Starting SeaweedFS Volume Server...${NC}"
-./weed volume -mserver=localhost:9333 -port=8080 -dir=/tmp/seaweedfs-volume &
+./weed volume -master=localhost:9333 -port=8080 -dir=/tmp/seaweedfs-volume &
 VOLUME_PID=$!
 wait_for_service "Volume Server" "http://localhost:8080/status"