Increase NFS server pod internal disk size to 20GB

longhorn/longhorn#11128

Signed-off-by: Roger Yao <roger.yao@suse.com>

Author: roger-ryao

manager/integration/deploy/backupstores/nfs-backupstore.yaml

@@ -58,7 +58,7 @@ spec:
         - name: PSEUDO_PATH
           value: /opt/backupstore
         - name: NFS_DISK_IMAGE_SIZE_MB
-          value: "4096"
+          value: "20480"
         command: ["bash", "-c", "chmod 700 /opt/backupstore && /opt/start_nfs.sh | tee /var/log/ganesha.log"]
         securityContext:
           privileged: true