Add posthog as a analytics component

## Issue Type

Please inform the type(s) of issue(s) you are reporting:

- Feature Request

## Description

Posthog is a well known data analytics tool. It would be nice to provide a simple way to integrate it with your application.

My proposal:
- [x] Add posthog script head
- [x] Add posthog to listen to deco events
- [ ] Allow easy integration with elements to capture click/actions (using data-attributes)

The last topic (data-attr) seems like something that we should rethink with a more overall approach (i.e. allow any html element to be tagged via engine).