Add GTFS Schedule Best Practices to GTFS Validator

[e-lo]

Is your feature request related to a problem? Please describe.
In order for the DRMT Transit Data Assessments Team to fully assess the GTFS Minimum Guidelines, they need to have access to validation reports which have the GTFS Best Practices.

Currently most best practices are not assessed in the GTFS Validator.

Describe the solution you'd like

• "Automatable" GTFS Best Practices added to the GTFS Validator. This list already exists in GTFS Schedule Validator repo.
• Metabase question which answers how many best practices are followed

Describe alternatives you've considered

• The "do nothing" alternative is to not assess compliance with the GTFS best practices

[holly-g]

First PR (resolving MobilityData/gtfs-validator#877) is up: MobilityData/gtfs-validator#1123

Up next:
MobilityData/gtfs-validator#885
MobilityData/gtfs-validator#930

cc @e-lo and @evansiroky

[lauriemerrell]

I believe that this need will ultimately be met by the current MD efforts to add best practices to the spec: google/transit#396, recommend closing this ticket.