Add FragmentsRendering to documentation for return values

Closes gh-33162

Author: rstoyanchev

framework-docs/modules/ROOT/pages/web/webflux/controller/ann-methods/return-types.adoc

@@ -68,6 +68,9 @@ Controllers can then return a `Flux<List<B>>`; Reactor provides a dedicated oper
 | `Rendering`
 | An API for model and view rendering scenarios.
 
+| `FragmentsRendering`, `Flux<Fragment>`, `Collection<Fragment>`
+| For rendering one or more fragments each with its own view and model.
+
 | `void`
 | A method with a `void`, possibly asynchronous (for example, `Mono<Void>`), return type (or a `null` return
   value) is considered to have fully handled the response if it also has a `ServerHttpResponse`,

framework-docs/modules/ROOT/pages/web/webmvc/mvc-controller/ann-methods/return-types.adoc

@@ -56,6 +56,9 @@ supported for all return values.
 | `ModelAndView` object
 | The view and model attributes to use and, optionally, a response status.
 
+| `FragmentsRendering`, `Collection<ModelAndView>`
+| For rendering one or more fragments each with its own view and model.
+
 | `void`
 | A method with a `void` return type (or `null` return value) is considered to have fully
   handled the response if it also has a `ServletResponse`, an `OutputStream` argument, or