docs: added info about cdn cache busting

Author: michaelKurowski

docs/content/4.sdk/2.getting-started/2.middleware-module.md

@@ -128,6 +128,7 @@ The `middlewareModule` accepts the following options:
 - `defaultRequestConfig` - (Optional) default request config for each request,
 - `httpClient` - (Optional) a custom HTTP client,
 - `errorHandler` - (Optional) a custom error handler for HTTP requests.
+- `cdnCacheBustingId` - (Optional) a middleware version identifier that will be attached to all `GET` requests for the sake of bypassing the CDN cache stored for a different version of the middleware.
 
 Example configuration:
 
@@ -150,6 +151,7 @@ export const sdk = initSDK({
     errorHandler: ({ error, methodName, url, params, config, httpClient }) => {
       // Custom error handler
     },
+    cdnCacheBustingId: // git commit hash of the monorepo where both middleware and the storefront is located
   }),
 });
 ```