Only raise a foreign key violation error when network_id is missing from both networks.txt and routes.txt

[qcdyx]

Describe the problem

The network_id field of GtfsFareLegRule is a foreign key that references routes.txt. If should reference both routes.txt and networks.txt. cc @tzujenchanmbd

Proposed solution

networkId is declared as a foreign key that references the network_id field in both the routes.txt and networks.txt tables.

Logic:

IF network_id exists in fare_leg_rules.txt but not in routes.txt OR networks.txt, generate a foreign_key_violation notice.

Alternatives you've considered

No response

Additional context

No response