docs: add documentation for remaining plugins (#4994)

* docs: add documentation for remaining plugins

* fix eslint errors

www/docs/content/plugins/other/discount-generator.md

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+---
+addHowToData: true
+---
+
+# Discount Generator
+
+In this document, you’ll learn how to install the Discount Generator plugin on your Medusa backend.
+
+## Overview
+
+In Medusa, merchants can create dynamic discounts that act as a template for other discounts. With dynamic discounts, merchants don't have to repeat certain conditions every time they want to create a new discount.
+
+The discount generator plugin allows merchants and developers to generate new discounts from a dynamic discount. This can be done either by envoking the `/discount-code` endpoint or using the `DiscountGeneratorService`.
+
+---
+
+## Prerequisites
+
+Before you follow this guide, you must have a Medusa backend installed. If not, you can follow the [quickstart guide](../../create-medusa-app.mdx) to learn how to do it.
+
+---
+
+## Install Plugin
+
+In the directory of your Medusa backend, run the following command to install the plugin:
+
+```bash npm2yarn
+npm install medusa-plugin-discount-generator
+```
+
+Finally, add the plugin to the `plugins` array in `medusa-config.js`:
+
+```js title=medusa-config.js
+const plugins = [
+  // ...
+  {
+    resolve: `medusa-plugin-discount-generator`,
+  },
+]
+```
+
+---
+
+## Test the Plugin
+
+### Using the Endpoint
+
+The plugin registers a `POST` endpoint `/discount-code`. The endpoint accepts in the request body the parameter `discount_code` which is a string indicating the code of the dynamic discount to generate a new discount from. The endpoint then creates the new discount from the dynamic discount and returns it in the response.
+
+So, to test out the endpoint, run the following command in the root of your project to start the Medusa backend:
+
+```bash
+npx medusa develop
+```
+
+Then, create a dynamic discount. You can do that either using the [Medusa admin](../../user-guide/discounts/create.mdx) which is available (if installed) at `http://localhost:7001` after starting the backend, or using the [Admin REST APIs](../../modules/discounts/admin/manage-discounts.mdx).
+
+After that, send a `POST` request to the `/discount-code` endpoint, passing the `discount_code` parameter in the request body with the value being the code of the dynamic discount you just created. A new discount will be created with the same attributes as the dynamic discount code and returned in the response.
+
+### Using the DiscountGeneratorService
+
+After installing the plugin, the `DiscountGeneratorService` is registered in the [dependency container](../../development/fundamentals/dependency-injection.md). So, you can resolve and use it in custom services, endpoints, or other resources.
+
+The `DiscountGeneratorService` has one method `generateDiscount`. This method requires passing the code of a dynamic discount as a parameter. It then creates a new discount having the same attributes as the dynamic discount, but with a different, random code.
+
+Here's an example of using the service in an endpoint:
+
+```ts title=src/api/index.ts
+import { Request, Response, Router } from "express"
+import bodyParser from "body-parser"
+
+export default (rootDirectory: string): Router | Router[] => {
+  const router = Router()
+
+  router.use(
+    "/generate-discount-code",
+    bodyParser.json(), 
+    async (req: Request, res: Response) => {
+    // skipping validation for simplicity
+    const { dynamicCode } = req.body
+    const discountGenerator = req.scope.resolve(
+      "discountGeneratorService"
+    )
+    const code = await discountGenerator.generateDiscount(
+      dynamicCode
+    )
+
+    res.json({
+      code,
+    })
+  })
+
+  return router
+}
+```