Investigate and add back template tracking in the editor_session_start event

[antonis]

Expected behavior

The template used during page creation is tracked in the editor_session_start event

Actual behavior

The template used during page creation is not tracked in the editor_session_start event

Steps to reproduce the behavior

1. Create a page using a template
2. Notice the editor_session_start event does not carry the template parameter

Extra context

The template parameter was introduced in #15038 and seems to be removed with #16155

Tested on iPhone SE 2020, iOS 14.4, WPiOS 18.0

[dangermattic]

Thanks for reporting! 👍