docs(server): 修正配置文件路径参数

- 将 -config 参数修正为 --config
- 更新了 server 结构体的文档注释

Author: zredb

src/cli/command/server.rs

@@ -42,7 +42,7 @@ server can respond to requests.
 
 Start a server with a configuration file:
 
-  $ rvault server -config=/etc/rvault/config.hcl"#
+  $ rvault server --config=/etc/rvault/config.hcl"#
 )]
 pub struct Server {
     #[deref]