[GTFS-Fares v2] Add fare_leg_join_rules.txt

[tzujenchanmbd]

This PR is based on Google's fare_leg_join_rules.txt proposal. At the workgroup meeting on February 27th, the following consensus was reached:

• Predicates for from_network_id and to_network_id will be added first, followed by the addition of other predicates such as from_stop_id and to_stop_id.
• from_network_id and to_network_id are required fields, and initially will be restricted to the same network_id. We will consider relaxing this for different network_id later.

Changes in this PR

• Add Effective Fare Leg in term definition
• Add fare_leg_join_rules.txt
• Modify network_id, from_area_id, to_area_id, from_timeframe_group_id, to_timeframe_group_id in fare_leg_rules.txt for effective fare leg

For previous discussions please see the working group meeting note and issue#346

Please go through the changes and feel free to share your thoughts/questions here.

[tzujenchanmbd]

In the October meeting, the working group reached a consensus to add from_stop_id and to_stop_id. (Meeting notes) Commits 4c978de & 32f3224 included these two fields. (Meeting notes)

During the meeting working group also recognized the potential for further expansion of this file in the future, including:

• Allowing joins across different networks
• Mechanism for negation

[tzujenchanmbd]

Hello,

We have at least one producer: Ito. They have shared their dataset extract in this file, which is part of a private feed.
We have at least one consumer: Google. Please see the screenshot below.

As per the GTFS amendment process, the requirements to open a vote are met.
We are opening a vote for adding fare_leg_join_rules.txt.

Voting ends on 2024-12-03 at 23:59:59 UTC.

[halbertram]

+1 from Ito

[westontrillium]

+1 from Trillium

[jfabi]

+1 from the @mbta

[tzujenchanmbd]

The vote passed on 2024-12-03 at 23:59:59 UTC.

3 votes in favour and no votes against.

Votes came from:
Ito (@halbertram)
Trillium (@westontrillium)
MBTA (@jfabi)

Thank you to everyone who participated!