Epic: add mart_gtfs tables based on data-analyses/gtfs_funnel work

[tiffanychu90]

User story / feature request

The data-analyses GTFS analytics pipeline has reached a point where the majority of GTFS data products are using the same upstream scripts to query, transform several mart_gtfs tables. Identify some tables to add into the warehouse, especially some of the scripts related to GTFS RT (vehicle positions).

Acceptance Criteria

• mart_gtfs.fct_vehicle_positions_dwell - gtfs_funnel/vp_dwell_time script
  • incorporate "dwell time" as a concept of how many vp are we counting at that same position, and use columns location_timestamp and moving_timestamp to identify when the bus first arrives at the location, when the bus starts moving again, and how many vehicle positions can be rolled up into 1 row. Based on work in data-analyses, a single day might be reduced from 15M rows to 12M rows.
  • MBTA repo

Add more tables as it comes up.