jte: model support

[jknack]

Add support for: https://jte.gg/jte-models

get("/static", ctx -> {
      var templates = new StaticTemplates();
      return templates.hello(new NavbarModel(), new WebsiteUrl(), "static");
});

get("/dynamic", ctx -> {
      var templates = new DynamicTemplates(require(TemplateEngine.class));
      return templates.hello(new NavbarModel(), new WebsiteUrl(), "dynamic");
});

See #3599