Remove the datetime field from delivery_acknowledgement and heartbeat events

[cortadocodes]

Feature request

Current state

We're about to have datetime duplicated for delivery_acknowledgement and heartbeat events (it's about to be added to the attributes of all events, so there's no need to keep it in the event too). To reduce confusion and event size, we should remove it from these events.

Proposed Solution

• Remove the datetime field from the delivery_acknowledgement and heartbeat events
• Update the event handler to utilise attributes as well as events