docs: added cart storefront guides (#7662)

* docs: added cart storefront guides

* add context guides

* small fixes to the context

www/apps/resources/app/storefront-development/regions/context/page.mdx

@@ -0,0 +1,171 @@
+import { CodeTabs, CodeTab } from "docs-ui"
+
+export const metadata = {
+  title: `Region Context in Storefront`,
+}
+
+# {metadata.title}
+
+Throughout your storefront, you'll need to access the selected region to perform different actions, such as retrieve product's prices in the selected region.
+
+So, if your storefront is React-based, create a region context and add it at the top of your components tree. Then, you can access the selected region anywhere in your storefront.
+
+## Create Region Context Provider
+
+For example, create the following file that exports a `RegionProvider` component and a `useRegion` hook:
+
+export const highlights = [
+  ["12", "region", "Expose region to children of the context provider."],
+  ["13", "setRegion", "Allow the context provider's children to change the selected region."],
+  ["24", "RegionProvider", "The provider component to use in your component tree."],
+  ["32", "", "If a region is set, set its ID in the local storage again in case it changed."],
+  ["39", "regionId", "Retrieve the selected region from the `localStorage`."],
+  ["42", "fetch", "If no region is selected, retrieve the list of regions from the Medusa application and select the first one."],
+  ["51", "fetch", "If a region is selected, retrieve it from the Medusa application."],
+  ["71", "useRegion", "The hook that child components of the provider use to access the region."]
+]
+
+```tsx highlights={highlights}
+"use client" // include with Next.js 13+
+
+import { 
+  createContext, 
+  useContext, 
+  useEffect, 
+  useState
+} from "react"
+import { HttpTypes } from "@medusajs/types"
+
+type RegionContextType = {
+  region?: HttpTypes.StoreRegion
+  setRegion: React.Dispatch<
+    React.SetStateAction<HttpTypes.StoreRegion | undefined>
+  >
+}
+
+const RegionContext = createContext<RegionContextType | null>(null)
+
+type RegionProviderProps = {
+  children: React.ReactNode
+}
+
+export const RegionProvider = (
+  { children }: RegionProviderProps
+) => {
+  const [region, setRegion] = useState<
+    HttpTypes.StoreRegion
+  >()
+
+  useEffect(() => {
+    if (region) {
+      // set its ID in the local storage in
+      // case it changed
+      localStorage.setItem("region_id", region.id)
+      return
+    }
+
+    const regionId = localStorage.getItem("region_id")
+    if (!regionId) {
+      // retrieve regions and select the first one
+      fetch(`http://localhost:9000/store/regions`, {
+        credentials: "include"
+      })
+      .then((res) => res.json())
+      .then(({ regions }) => {
+        setRegion(regions[0])
+      })
+    } else {
+      // retrieve selected region
+      fetch(`http://localhost:9000/store/regions/${regionId}`, {
+        credentials: "include"
+      })
+      .then((res) => res.json())
+      .then(({ region: dataRegion }) => {
+        setRegion(dataRegion)
+      })
+    }
+  }, [region])
+
+  return (
+    <RegionContext.Provider value={{
+      region,
+      setRegion
+    }}>
+      {children}
+    </RegionContext.Provider>
+  )
+}
+
+export const useRegion = () => {
+  const context = useContext(RegionContext)
+
+  if (!context) {
+    throw new Error("useRegion must be used within a RegionProvider")
+  }
+
+  return context
+}
+```
+
+The `RegionProvider` handles retrieving the selected region from the Medusa application, and updating its ID in the `localStorage`.
+
+The `useRegion` hook returns the value of the `RegionContext`. Child components of `RegionProvider` use this hook to access `region` or `setRegion`.
+
+---
+
+## Use RegionProvider in Component Tree
+
+To use the region context's value, add the `RegionProvider` high in your component tree.
+
+For example, if you're using Next.js, add it to the `app/layout.tsx` or `src/app/layout.tsx` file:
+
+```tsx title="app/layout.tsx" collapsibleLines="1-14" highlights={[["22"]]}
+import type { Metadata } from "next"
+import { Inter } from "next/font/google"
+import "./globals.css"
+import { CartProvider } from "../providers/cart"
+import { RegionProvider } from "../providers/region"
+
+const inter = Inter({ subsets: ["latin"] });
+
+export const metadata: Metadata = {
+  title: "Create Next App",
+  description: "Generated by create next app",
+};
+
+export default function RootLayout({
+  children,
+}: Readonly<{
+  children: React.ReactNode;
+}>) {
+  return (
+    <html lang="en">
+      <body className={inter.className}>
+        <RegionProvider>
+          {/* Other providers... */}
+          {children}
+        </RegionProvider>
+      </body>
+    </html>
+  );
+}
+```
+
+---
+
+## Use useRegion Hook
+
+Now, you can use the `useRegion` hook in child components of `RegionProvider`.
+
+For example:
+
+```tsx
+"use client" // include with Next.js 13+
+// ...
+import { useRegion } from "../providers/region"
+
+export default function Products() {
+  const { region } = useRegion()
+  // ...
+}
+```