Add Stop Access feature

[skalexch]

Describe the problem

Since we adopted stop_access, we should include it as a feature.

Base Add-ons -> Stop Access (for now). Ideally under "Location Types".

Proposed solution

If the field stop_access exists for at least one entry in stops.txt, then the Stop Access feature exists.

Alternatives you've considered

No response

Additional context

No response

[qcdyx]

Hi @skalexch are you planning to add documentation for Stop Access feature as well? It's not listed here: https://gtfs.org/getting-started/features/base-add-ons/#location-types

[skalexch]

@qcdyx yes, I am drafting it along with Cars Allowed. @Sergiodero is drafting cEMV support.