Hi there, how can I get ga_session_id and ga_session_number

## What feature would you like to see?

I want to get `ga_session_id` and `ga_session_number` for each event in Android/iOS client. How can I get these values?

## How would you use it?

We are trying to align the number of user sessions between Segment and Google Analytics.
Google Analytics is calculating session using ga_session_id and ga_session_number parameter
having these parameters helps DE align the number of user sessions
it should be retrievable from firebase SDK.

So we will add `ga_session_id` and `ga_session_number` we track any event, and send it both to analytics, segment...
After that, we can easily analyze.