[Reader] Add number of followed sites and tags to Reader analytics

On Android, we aimed to avoid adding a new network call to fetch the number of subscriptions/tags. Therefore, we integrated with the existing logic that synchronizes tags and sites, triggering a new analytics event for this purpose. This approach serves as an initial step to incorporate this data into our analytics without extra fetches on screens where this information isn't displayed, thereby minimizing data usage and potential performance issues, while ensuring we track the most current information.

Event name: reader_following_fetched
Properties:

• type (String): either sites or tags.
• count (int): number of following sites or tags (depending on type).

Note: When synching the number of sites, we should use the field total_subscriptions returned by the API https://developer.wordpress.com/docs/api/1.2/get/read/following/mine/

No file or test is named. Start by locating the existing Reader logic that synchronizes followed sites and tags, then review how analytics events are emitted and how the API exposes total_subscriptions. Done means emitting reader_following_fetched for sites and tags with the correct type and count without adding a separate network call.