Document i18n locale limit (vercel#27542)

Add check for i18n locale count and ensure the limit is documented

## Documentation / Examples

- [x] Make sure the linting passes

docs/advanced-features/i18n-routing.md

@@ -281,3 +281,8 @@ export const getStaticPaths = ({ locales }) => {
   }
 }
 ```
+
+## Limits for the i18n config
+
+- `locales`: 100 total locales
+- `domains`: 100 total locale domain items

errors/invalid-i18n-config.md

@@ -2,11 +2,11 @@
 
 #### Why This Error
 
-In your `next.config.js` file you provided an invalid config for the `i18n` field.
+In your `next.config.js` file you provided an invalid config for the `i18n` field. This could mean the limit for 100 locale items was exceeded.
 
 #### Possible Ways to Fix It
 
-Make sure your `i18n` field follows the allowed config shape and values:
+Make sure your `i18n` field follows the allowed config shape, limits, and values:
 
 ```js
 module.exports = {

packages/next/server/config.ts

@@ -320,6 +320,12 @@ function assignDefaults(userConfig: { [key: string]: any }) {
       )
     }
 
+    if (i18n.locales.length > 100) {
+      throw new Error(
+        `Received ${i18n.locales.length} i18n.locales items which exceeds the max of 100, please reduce the number of items to continue.\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`
+      )
+    }
+
     const defaultLocaleType = typeof i18n.defaultLocale
 
     if (!i18n.defaultLocale || defaultLocaleType !== 'string') {