Support for event deduplication

[joandvgv]

Hi all! I noticed the current track event is not sending the id as part of the payload so the event deduplication feature is not working.

This should do the fix, am I right?

Can update formatting or attend any request from repository owners if this PR makes sense.

Thank you!

[newhook]

Hey Joan , thanks for the PR. However, won't this break existing code which passes "id" as part of the data payload? For example, consider:

cio = CustomerIO(site_id, api_key, region=Regions.US)
cio.track(customer_id="5", name='purchased', id='item_47', price=2.25)