docs: add routing page (#9550)

- Add a new homepage to `book` project for the routing page
- Move all main doc pages to be under `/v2/learn` (and added redirects + fixed links across docs)
- Other: add admin components to resources dropdown + fixes to search on mobile.

Closes DX-955

Preview: https://docs-v2-git-docs-router-page-medusajs.vercel.app/v2

www/apps/book/app/learn/advanced-development/api-routes/parameters/page.mdx

@@ -0,0 +1,155 @@
+export const metadata = {
+  title: `${pageNumber} API Route Parameters`,
+}
+
+# {metadata.title}
+
+In this chapter, you’ll learn about path, query, and request body parameters.
+
+## Path Parameters
+
+To create an API route that accepts a path parameter, create a directory within the route file's path whose name is of the format `[param]`.
+
+For example, to create an API Route at the path `/hello-world/:id`, where `:id` is a path parameter, create the file `src/api/hello-world/[id]/route.ts` with the following content:
+
+export const singlePathHighlights = [
+  ["11", "req.params.id", "Access the path parameter `id`"]
+]
+
+```ts title="src/api/hello-world/[id]/route.ts" highlights={singlePathHighlights}
+import type {
+  MedusaRequest,
+  MedusaResponse,
+} from "@medusajs/framework/http"
+
+export const GET = async (
+  req: MedusaRequest,
+  res: MedusaResponse
+) => {
+  res.json({
+    message: `[GET] Hello ${req.params.id}!`,
+  })
+}
+```
+
+The `MedusaRequest` object has a `params` property. `params` holds the path parameters in key-value pairs.
+
+### Multiple Path Parameters
+
+To create an API route that accepts multiple path parameters, create within the file's path multiple directories whose names are of the format `[param]`.
+
+For example, to create an API route at `/hello-world/:id/name/:name`, create the file `src/api/hello-world/[id]/name/[name]/route.ts` with the following content:
+
+export const multiplePathHighlights = [
+  ["12", "req.params.id", "Access the path parameter `id`"],
+  ["13", "req.params.name", "Access the path parameter `name`"]
+]
+
+```ts title="src/api/hello-world/[id]/name/[name]/route.ts" highlights={multiplePathHighlights}
+import type {
+  MedusaRequest,
+  MedusaResponse,
+} from "@medusajs/framework/http"
+
+export const GET = async (
+  req: MedusaRequest,
+  res: MedusaResponse
+) => {
+  res.json({
+    message: `[GET] Hello ${
+      req.params.id
+    } - ${req.params.name}!`,
+  })
+}
+```
+
+You access the `id` and `name` path parameters using the `req.params` property.
+
+---
+
+## Query Parameters
+
+You can access all query parameters in the `query` property of the `MedusaRequest` object. `query` is an object of key-value pairs, where the key is a query parameter's name, and the value is its value.
+
+For example:
+
+export const queryHighlights = [
+  ["11", "req.query.name", "Access the query parameter `name`"],
+]
+
+```ts title="src/api/hello-world/route.ts" highlights={queryHighlights}
+import type {
+  MedusaRequest,
+  MedusaResponse,
+} from "@medusajs/framework/http"
+
+export const GET = async (
+  req: MedusaRequest,
+  res: MedusaResponse
+) => {
+  res.json({
+    message: `Hello ${req.query.name}`,
+  })
+}
+```
+
+The value of `req.query.name` is the value passed in `?name=John`, for example.
+
+---
+
+## Request Body Parameters
+
+The Medusa application parses the body of any request having its `Content-Type` header set to `application/json`. The request body parameters are set in the `MedusaRequest`'s `body` property.
+
+For example:
+
+export const bodyHighlights = [
+  ["11", "HelloWorldReq", "Specify the type of the request body parameters."],
+  ["15", "req.body.name", "Access the request body parameter `name`"],
+]
+
+```ts title="src/api/hello-world/route.ts" highlights={bodyHighlights}
+import type {
+  MedusaRequest,
+  MedusaResponse,
+} from "@medusajs/framework/http"
+
+type HelloWorldReq = {
+  name: string
+}
+
+export const POST = async (
+  req: MedusaRequest<HelloWorldReq>,
+  res: MedusaResponse
+) => {
+  res.json({
+    message: `[POST] Hello ${req.body.name}!`,
+  })
+}
+```
+
+In this example, you use the `name` request body parameter to create the message in the returned response.
+
+<Note title="Tip">
+
+The `MedusaRequest` type accepts a type argument that indicates the type of the request body. This is useful for auto-completion and to avoid typing errors.
+
+</Note>
+
+To test it out, send the following request to your Medusa application:
+
+```bash
+curl -X POST 'http://localhost:9000/hello-world' \
+-H 'Content-Type: application/json' \
+--data-raw '{
+  "name": "John"
+}'
+```
+
+This returns the following JSON object:
+
+```json
+{
+  "message": "[POST] Hello John!"
+}
+```