ADR & `event_udp_to_kafka`: `frame_sync_delay` corrections

In `event_udp_to_kafka`, we need to apply corrections for data that has been collected with a `frame_sync_delay`.

The basic correction required is to:
- *Subtract* the `frame_sync_delay` from the GpsTime in the header before putting it into the `reference_time` of an `ev44`.
- *Add* the `frame_sync_delay` to the timestamp of each individual neutron event

Write an ADR that describes our handling of `frame_sync_delay` and long frames etc.