api: move config/user to access/users, implement change_password

To make it similar to the pve api

src/api2/config.rs

@@ -3,12 +3,10 @@ use proxmox::list_subdirs_api_method;
 
 pub mod datastore;
 pub mod remote;
-pub mod user;
 
 const SUBDIRS: SubdirMap = &[
     ("datastore", &datastore::ROUTER),
     ("remote", &remote::ROUTER),
-    ("user", &user::ROUTER),
 ];
 
 pub const ROUTER: Router = Router::new()