New Rule Proposal: Individual TripUpdate timestamp missing/stale

[evansiroky]

Summary:

A warning should be raised for each individual TripUpdate entity that has a missing or stale timestamp.

Steps to reproduce:

Given a TripUpdate dataset
When the validator checks an individual TripUpdate record and detects that the timestamp is missing or stale
Then the validator should flag this respective TripUpdate in question for having a missing or stale timestamp set

Expected behavior:

The GTFS-Realtime Best Practices state:

Data within a GTFS Realtime feed should not be older than 90 seconds for Trip Updates and Vehicle Positions and not older than 10 minutes for Service Alerts.

The GTFS Validator should flag all TripUpdates individually that do not have a timestamp value added or one that is added but is far enough in the past that it is stale.

Observed behavior:

Timestamps are currently only checked at the feed-level.