docs: document analytics module (#12563)

www/apps/book/app/learn/fundamentals/modules/infrastructure-modules/page.mdx

@@ -20,6 +20,7 @@ There are different Infrastructure Module types including:
 
 ![Diagram illustrating how the modules connect to third-party services](https://res.cloudinary.com/dza7lstvk/image/upload/v1727095814/Medusa%20Book/architectural-modules_bj9bb9.jpg)
 
+- Analytics Module: Integrates a third-party service to track and analyze user interactions and system events.
 - Cache Module: Defines the caching mechanism or logic to cache computational results.
 - Event Module: Integrates a pub/sub service to handle subscribing to and emitting events.
 - Workflow Engine Module: Integrates a service to store and track workflow executions and steps.

www/apps/book/app/learn/introduction/architecture/page.mdx

@@ -71,6 +71,7 @@ You can replace any of the third-party services mentioned above to build your pr
 
 [Infrastructure Modules](!resources!/infrastructure-modules) integrate third-party services and systems that customize Medusa's infrastructure. Medusa has the following Infrastructure Modules:
 
+- [Analytics Module](!resources!/infrastructure-modules/analytics): Tracks and analyzes user interactions and system events with third-party analytic providers. You can integrate [PostHog](!resources!/infrastructure-modules/analytics/posthog) as the analytics provider.
 - [Cache Module](!resources!/infrastructure-modules/cache): Caches data that require heavy computation. You can integrate a custom module to handle the caching with services like Memcached, or use the existing [Redis Cache Module](!resources!/infrastructure-modules/cache/redis).
 - [Event Module](!resources!/infrastructure-modules/event): A pub/sub system that allows you to subscribe to events and trigger them. You can integrate [Redis](!resources!/infrastructure-modules/event/redis) as the pub/sub system.
 - [File Module](!resources!/infrastructure-modules/file): Manages file uploads and storage, such as upload of product images. You can integrate [AWS S3](!resources!/infrastructure-modules/file/s3) for file storage.