Add password_hints_allowed config option

Disabling password hints is mainly useful for admins who are concerned that
their users might provide password hints that are too revealing.

src/config.rs

@@ -436,6 +436,8 @@ make_config! {
         /// Password iterations |> Number of server-side passwords hashing iterations.
         /// The changes only apply when a user changes their password. Not recommended to lower the value
         password_iterations:    i32,    true,   def,    100_000;
+        /// Allow password hints |> Controls whether users can set password hints. This setting applies globally to all users.
+        password_hints_allowed: bool,   true,   def,    true;
         /// Show password hint |> Controls whether a password hint should be shown directly in the web page
         /// if SMTP service is not configured. Not recommended for publicly-accessible instances as this
         /// provides unauthenticated access to potentially sensitive data.