fix: expose arrow id for shuttle stops view

[meagharty]

Summary of changes

Asana Ticket: Relates to importing shuttles

Expose arrow id field so that we can use it to bulk update Arrow shuttle stops. In other situations, we can use stop_id under the stop's attributes

Reviewer Checklist

• Meets ticket's acceptance criteria
• Any new or changed functions have typespecs
• Tests were added for any new functionality (don't just rely on Codecov)
• This branch was deployed to the staging environment and is currently running with no unexpected increase in warnings, and no errors or crashes.

[jzimbel-mbta]

Looks good and makes sense to me!