docs: add fastify-delay-request (fastify#4569)

* docs: add fastify-delay-request

The plugin that implement fastify#2500 using `p-queue`.

The test is flaky, I have no idea why `macOS` failed. 
But the implementation should be good enough for production use.

* chore: update plugin description

Co-authored-by: Frazer Smith <[email protected]>

---------

Co-authored-by: Frazer Smith <[email protected]>

Author: climba03003

docs/Guides/Ecosystem.md

@@ -282,6 +282,9 @@ section.
   functions.
 - [`fastify-decorators`](https://github.com/L2jLiga/fastify-decorators) Fastify
   plugin that provides the set of TypeScript decorators.
+- [`fastify-delay-request`](https://github.com/climba03003/fastify-delay-request)
+  Fastify plugin that allows requests to be delayed whilst a task the response is
+  dependent on is run, such as a resource intensive process.
 - [`fastify-disablecache`](https://github.com/Fdawgs/fastify-disablecache)
   Fastify plugin to disable client-side caching, inspired by
   [nocache](https://github.com/helmetjs/nocache).