plugins/lsp: enable ltex_plus

ltex_plus settingsOptions based on those for ltex, but modified to
align with changes in ltex_plus

Author: Kirens

plugins/lsp/language-servers/default.nix

@@ -38,6 +38,10 @@ let
       settingsOptions = import ./ltex-settings.nix { inherit lib helpers; };
       settings = cfg: { ltex = cfg; };
     };
+    ltex_plus = {
+      settingsOptions = import ./ltex-plus-settings.nix { inherit lib helpers; };
+      settings = cfg: { ltex = cfg; };
+    };
     lua_ls = {
       settingsOptions = import ./lua-ls-settings.nix { inherit lib helpers; };
       settings = cfg: { Lua = cfg; };